Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C11/00—Regeneration of pulp liquors or effluent waste waters
  • D21C11/0064—Aspects concerning the production and the treatment of green and white liquors, e.g. causticizing green liquor
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C11/00—Regeneration of pulp liquors or effluent waste waters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F27/00—Mixers with rotary stirring devices in fixed receptacles; Kneaders
  • B01F27/40—Mixers with rotor-rotor system, e.g. with intermeshing teeth
  • B01F27/41—Mixers with rotor-rotor system, e.g. with intermeshing teeth with the mutually rotating surfaces facing each other
  • B01F27/411—Mixers with rotor-rotor system, e.g. with intermeshing teeth with the mutually rotating surfaces facing each other provided with intermeshing elements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
  • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
  • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
  • B09B3/70—Chemical treatment, e.g. pH adjustment or oxidation
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F11/00—Compounds of calcium, strontium, or barium
  • C01F11/18—Carbonates
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F11/00—Treatment of sludge; Devices therefor
  • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
  • C02F11/14—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents
  • C02F11/148—Combined use of inorganic and organic substances, being added in the same treatment step
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F5/00—Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
  • C02F5/02—Softening water by precipitation of the hardness
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F9/00—Multistage treatment of water, waste water or sewage
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C11/00—Regeneration of pulp liquors or effluent waste waters
  • D21C11/0007—Recovery of by-products, i.e. compounds other than those necessary for pulping, for multiple uses or not otherwise provided for
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C11/00—Regeneration of pulp liquors or effluent waste waters
  • D21C11/0042—Fractionating or concentration of spent liquors by special methods
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C11/00—Regeneration of pulp liquors or effluent waste waters
  • D21C11/0064—Aspects concerning the production and the treatment of green and white liquors, e.g. causticizing green liquor
  • D21C11/0078—Treatment of green or white liquors with other means or other compounds than gases, e.g. in order to separate solid compounds such as sodium chloride and carbonate from these liquors; Further treatment of these compounds
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C11/00—Regeneration of pulp liquors or effluent waste waters
  • D21C11/0085—Introduction of auxiliary substances into the regenerating system in order to improve the performance of certain steps of the latter, the presence of these substances being confined to the regeneration cycle
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C11/00—Regeneration of pulp liquors or effluent waste waters
  • D21C11/04—Regeneration of pulp liquors or effluent waste waters of alkali lye
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F2215/00—Auxiliary or complementary information in relation with mixing
  • B01F2215/04—Technical information in relation with mixing
  • B01F2215/0413—Numerical information
  • B01F2215/0418—Geometrical information
  • B01F2215/0431—Numerical size values, e.g. diameter of a hole or conduit, area, volume, length, width, or ratios thereof
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
  • B01F2215/00—Auxiliary or complementary information in relation with mixing
  • B01F2215/04—Technical information in relation with mixing
  • B01F2215/0413—Numerical information
  • B01F2215/0436—Operational information
  • B01F2215/0481—Numerical speed values
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/001—Processes for the treatment of water whereby the filtration technique is of importance
  • C02F1/004—Processes for the treatment of water whereby the filtration technique is of importance using large scale industrial sized filters
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/02—Treatment of water, waste water, or sewage by heating
  • C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
  • C02F1/048—Purification of waste water by evaporation
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
  • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F2001/5218—Crystallization
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/20—Heavy metals or heavy metal compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
  • C02F2103/26—Nature of the water, waste water, sewage or sludge to be treated from the processing of plants or parts thereof
  • C02F2103/28—Nature of the water, waste water, sewage or sludge to be treated from the processing of plants or parts thereof from the paper or cellulose industry
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F3/00—Biological treatment of water, waste water, or sewage
  • C02F3/02—Aerobic processes
  • C02F3/12—Activated sludge processes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P40/00—Technologies relating to the processing of minerals
  • Y02P40/40—Production or processing of lime, e.g. limestone regeneration of lime in pulp and sugar mills
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W10/00—Technologies for wastewater treatment
  • Y02W10/10—Biological treatment of water, waste water, or sewage

Definitions

• the present disclosure relates to a method and system for the treatment of calcium-containing solid side stream material obtainable from a chemical recovery process of a chemical pulping process and to products obtainable therefrom.
• a method for the treatment of calcium- containing solid side stream material obtainable from a chemical recovery process of a chemical pulping process is disclosed.
• the method may comprise treating the calcium-containing solid side stream material with an acid, thereby obtaining a solution comprising a calcium and/or magnesium salt of the acid.
• Fig. 1 illustrates a method and a system for the treatment of calcium-containing solid side stream material
• Fig. 2A illustrates a cross-sectional side view of an embodiment of a high shear mixer
• Fig. 2B shows the same embodiment of the high shear mixer as a cross-sectional top view
• Fig. 3 shows EDS results of a dried liquid fraction (salt product) ;
• Fig. 4 shows sulphate and nitrate contents of samples of the dried liquid fraction (salt product) ;
• Fig. 5 shows ICP results from the same samples ;
• Fig. 6 illustrates EDS results of salt products
• Fig. 7 shows ICP results of salt products
• Fig. 8 shows EDS results of samples of salt products
• Fig. 9 illustrates ICP results of samples of salt products
• Fig. 10 shows EDS results of samples of salt products
• Fig. 11 shows ICP results of salt liquids
• Fig. 12 shows IC results of salt liquids
• Fig. 13 shows ICP results of salt liquids
• Fig. 14A and 14B illustrate EDS results of two trial points
• Fig. 15 shows acetate, sulphate and nitrate contents of the formed salt liquids analysed by IC.
• calcium-containing solid side stream materials such as green liquor dregs typically have a relatively high water content and may have a relatively high content of certain components, for example impurities such as heavy metals.
• Such calcium-containing solid side stream materials may, however, be treated with an acid to obtain a solution containing a calcium and/or magnesium salt of the acid.
• the solution may be used for various purposes, or the calcium and/or magnesium salt may be precipitated or crystallized therefrom and recycled or reused for various purposes. This can significantly reduce the amount of solid waste to be disposed of e.g. to landfills and lower the environmental impact of the calcium-containing solid side stream material.
• the method may also provide a process to separate a useful fraction from a less attractive or useful fraction of the calcium- containing solid side stream material.
• lime mud typically has a composition that makes it relatively well suitable for recycling and reuse. According to some embodiments of the method, it may be possible to reduce the use of lime mud, which may then be recycled in other ways .
• a method for the treatment of calcium- containing solid side stream material obtainable from a chemical recovery process of a chemical pulping process is disclosed.
• the term "calcium-containing solid side stream material” may be understood as referring to a calcium-containing solid side stream material obtainable from a chemical recovery process of a chemical pulping process.
• the calcium-containing solid side stream material may be any solid side stream material obtainable from a chemical recovery process of a chemical pulping process, for instance a causticizing process, provided it contains calcium.
• the calcium contained in the solid side stream material may be e.g. in the form of calcium carbonate (CaCO 3 ) , calcium oxide (CaO) , calcium hydroxide (Ca(OH) 2 ), and/or any mixture or combination thereof.
• Suitable calcium-containing solid side stream materials may comprise green liquor dregs, calcium carbonate containing solid side stream material, calcium oxide containing solid side stream material, fly ash, or any mixture or combination thereof.
• Other suitable calcium-containing solid side stream materials may comprise or be e.g. lime mud, lime slaker grits, solid side stream material obtainable from purification of flue gas from lime sludge reburning, burnt lime and any mixtures thereof.
• the calcium-containing solid side stream material may further contain magnesium.
• the calcium- containing solid side stream material may comprise various other components derived from the raw material for pulping, such as wood; for instance magnesium in the form of carbonate, oxide or hydroxide, aluminium, phosphorus (e.g. in the form of phosphates), manganese, sodium, sulphur, silicon, iron, zinc, various heavy metals, incombustible material, such as material derived from lignin, and/or any mixtures or combinations thereof.
• the calcium-containing solid side stream material may be a fraction that is (without the treatment with the acid) be considered a calcium- containing solid waste.
• the calcium-containing solid side stream material comprises or is green liquor dregs.
• the method may be particularly useful for the treatment of green liquor dregs, which are a complex side stream material to dispose and/or to treat further .
• Green liquor dregs may, in principle, refer to any solid matter separated from green liquor.
• Green liquor dregs may be formed when the molten smelt from a recovery boiler is dissolved in weak liquor (weak wash) to produce green liquor.
• Suspended particles, i.e. the solid matter, in the green liquor are referred to as dregs and are typically removed in a clarifier.
• Such solid matter may thus be separated from green liquor using a clarifier.
• green liquor dregs removed in a sedimentation clarifier or another type of clarifier may be filtered and washed to increase the solid content of the cake containing the green liquor dregs.
• Solid matter separated from green liquor may be obtainable by filtering using a filter, for example a drum filter, pre-coated with lime mud, or a filter belt press. Green liquor dregs separated using a clarifier may further be filtered. Various other methods and apparatuses for separating the solid matter may also be contemplated.
• Green liquor dregs may therefore refer, additionally or alternatively, to solid matter separated by filtering green liquor using a filter, for example a drum filter, precoated with lime mud.
• GLD may therefore optionally comprise lime mud.
• a calcium-containing solid side stream material comprising green liquor dregs and lime mud may also be referred to as "GLD to landfill".
• the GLD to landfill may, in an embodiment, be obtainable by filtering using a filter pre-coated with lime mud.
• Green liquor dregs may, additionally or alternatively, be obtained by filtering green liquor and/or green liquor dregs separated using a clarifier, using a suitable filter without the use of lime mud. For example, they can be separated by pressure filtration or using a decanter centrifuge. Green liquor dregs separated without the use of lime mud may be referred to as "green liquor dregs to filter". With pressure filtration, it may be possible to reach a relatively high dry solids content. With pressure filtration, it may also be possible to return more sodium back to the circulation of chemicals of the chemical pulping process.
• the calcium-containing solid side stream material comprises green liquor dregs, calcium carbonate containing solid side stream material, calcium oxide containing solid side stream material, fly ash, and/or any mixture or combination thereof.
• the green liquor dregs may be pressure filtered and optionally washed prior to treating them with the acid.
• they may be pressure filtered using a vertical pressure filtration unit and optionally washed prior to treating them with the acid.
• Green liquor dregs with a relatively high solids content may thereby be obtained, for example a solids content of at least 60 % (w/w) . It may also allow returning more sodium to the circulation of chemicals of the chemical pulping process.
• the pressure filtering and the washing after the filtering may significantly decrease the amount of sodium ending up in the GLD cake after filtering. Further, a smaller amount of acid may be required.
• the method may comprise treating the calcium- containing solid side stream material with an acid, thereby obtaining a solution comprising a calcium and/or magnesium salt of the acid.
• the calcium-containing solid side stream material and the acid are brought into contact. They may thus react, and the acid may dissolve at least a part of the calcium-containing solid side stream material, in particular at least a part of the calcium carbonate (CaCO 3 ) , magnesium carbonate (MgCO 3 ) , calcium oxide (CaO) , magnesium oxide (MgO) , calcium hydroxide (Ca(OH) 2 ), magnesium hydroxide (Mg(OH) 2 ), or any mixture or combination thereof, contained in the calcium-containing solid side stream material.
• the calcium and/or magnesium salt of the acid may be soluble in aqueous solutions, so that when the acid is added e.g. as an aqueous solution and/or when the calcium-containing solid side stream material in a slurried form is contacted with the acid, the solution is formed. It may therefore be understood that as the acid and the calcium-containing solid side stream material are mixed or slurried, the mixture or slurry may contain an amount of the resulting solution. Depending on the solubility of the calcium and/or magnesium salt of the acid, at least a part of the calcium and/or magnesium salt of the acid or possibly even the entire calcium and/or magnesium salt of the acid may be dissolved in the solution.
• Some calcium and/or magnesium salts such as calcium sulphate, may be less readily soluble. Parts of the calcium- containing solid side stream material which do not dissolve and/or react may remain as residual solids. In other words, both the solution and residual solids may be obtainable by the method.
• the method may be a continuous and/or an online method. It may be performed at an industrial scale .
• the acid may comprise or be nitric acid (HNO 3 ) ; sulphuric acid (H 2 SO 4 ) ; phosphoric acid (H 3 PO 4 ) ; an organic acid; or any combination or mixture thereof.
• examples of possible organic acids include carboxylic acids, such as acetic acid (CH 3 COOH) , citric acid, formic acid (HCOOH) , gluconic acid, lactic acid, oxalic acid, tartaric acid, or any mixtures or combinations thereof.
• the acid may be an aqueous solution of the acid, including any acids described above.
• the concentration of the aqueous solution of the acid may be selected such that a desired pH and/or volume of the slurry and/or solution is achieved.
• a concentrated acid solution for example a concentrated sulphuric acid or nitric acid, may be used so as to avoid introducing large volumes of water into the solution (or slurry, as described below) .
• the acid is an acid other than hydrochloric acid (HC1) , or an acid other than a hydrogen halide.
• the acid comprises at least one of nitric acid, an organic acid, or any combination or mixture thereof.
• the acid comprises nitric acid (HNO 3 ) , an organic acid or any mixture or combination thereof.
• the acid comprises nitric acid (HNO 3 ) , acetic acid (CH 3 COOH) or any mixture or combination thereof.
• the calcium salt of the acid may comprise one or more calcium salts of the acid(s), depending on the acid or acids used.
• the calcium salt of the acid may comprise calcium nitrate (Ca(NO 3 ) 2 ); calcium sulphate (CaSO 4 , which may be anhydrous or a hydrate in solid form) ; calcium phosphate (Ca 2+ combined with PO 4 3- , HPO 4 2- , and/or H 2 PO 4 -) ; a calcium salt of an organic acid; or any combination or mixture thereof.
• Examples of possible salts of organic acids include calcium salts of carboxylic acids, such as calcium acetate (Ca (CH 3 COO) 2 , which may be anhydrous or monohydrate in solid form) ; calcium citrate, calcium formate (Ca(HCOO) 2 ), calcium gluconate, calcium lactate, calcium oxalate, calcium tartrate, or any mixtures or combinations thereof.
• carboxylic acids such as calcium acetate (Ca (CH 3 COO) 2 , which may be anhydrous or monohydrate in solid form) ; calcium citrate, calcium formate (Ca(HCOO) 2 ), calcium gluconate, calcium lactate, calcium oxalate, calcium tartrate, or any mixtures or combinations thereof.
• the calcium-containing solid side stream material may further comprise other components than calcium carbonate, for example carbonates of magnesium and/or sodium.
• the solution may therefore also comprise magnesium (Mg) salts of the acid and/or sodium (Na) salts of the acid.
• Mg and/or Na salts may be salts of any of the acids described above.
• the term "calcium and/or magnesium salt” may therefore refer to a calcium salt; to a magnesium salt; or to a calcium salt and optionally a magnesium salt.
• the magnesium salt of the acid may, likewise, comprise one or more magnesium salts of the acid(s), depending on the acid or acids used.
• the magnesium salt of the acid may comprise magnesium nitrate (Mg(NO 3 ) 2 ); magnesium sulphate (MgSO 4 , which may be anhydrous or a hydrate in solid form) ; magnesium phosphate (Mg 2+ combined with PO 4 3- , HPO 4 2- , and/or H 2 PO 4 -) ; a magnesium salt of an organic acid; or any combination or mixture thereof.
• Examples of possible salts of organic acids include magnesium salts of carboxylic acids, such as magnesium acetate (Mg (CH 3 COO) 2 , which may be anhydrous or monohydrate in solid form) ; magnesium citrate, magnesium formate (Mg(HCOO) 2 ), magnesium gluconate, magnesium lactate, magnesium oxalate, magnesium tartrate, or any mixtures or combinations thereof.
• magnesium acetate Mg (CH 3 COO) 2
• magnesium citrate magnesium formate
• magnesium gluconate magnesium lactate
• magnesium oxalate magnesium tartrate
• the calcium-containing solid side stream material is treated with the acid
• the calcium- containing solid side stream material is contacted with the acid so that the acid and one or more components of the calcium-containing solid side stream material may react.
• They may be allowed to react for a certain reaction time. For example, they may, in some embodiments, be allowed to react for up to about 60 minutes, or for at least about 30 minutes, or for about 30 to about 60 minutes.
• the reaction time may depend e.g. on the mixing. When using a high shear mixer, as described below, the reaction time may be much shorter, for example about 3 to 5 seconds.
• At least a part of the calcium-containing solid side stream material may then dissolve into the solution, such that the solution formed comprises a calcium and/or magnesium salt of the acid (the calcium of the salt being derived from the calcium-containing solid side stream material) .
• the acid is either nitric acid or acetic acid and the calcium-containing solid side stream material comprises calcium carbonate:
• the method may comprise mixing the calcium- containing solid side stream material in a dry or slurried form with the acid and optionally with water to obtain a slurry.
• the volume and/or consistency of the slurry may be adjusted.
• the concentration of the aqueous solution of the acid may be selected such that a desired consistency of the slurry is achieved.
• water may be added to the slurry and/or to the calcium-containing solid side stream material to adjust its volume and/or consistency. Adding water to adjust the volume may improve dissolution of the calcium-containing solid side stream material, in particular in embodiments in which a high shear mixer, such as an Atrex-type mixer, is used.
• the slurry may also comprise the resulting solution.
• the (relative) amount of the solution obtained may increase in the slurry, and the (relative) amount of the calcium-containing solid side stream material and the acid may decrease.
• the slurry may also comprise residual solids that are not dissolved during the treatment.
• the surface area of the calcium-containing solid side stream material may be increased before or during mixing it with the acid.
• the calcium-containing solid side stream material may be preground prior to treating it with the acid. The pregrinding may increase the rate and/or extent the reaction between the calcium-containing solid side stream material and the acid.
• the pH of the slurry may be adjusted to a pH of 5 or lower, or to a pH in the range of about 2 to about 5.
• the pH may be such that the calcium- containing solid side stream material dissolves and/or reacts to a sufficient extent and/or at a sufficient rate.
• the pH may further be such that the solubility of certain components, for example heavy metals such as Cd, is minimized.
• a lower pH may be associated with improved removal of heavy metals, such as Cd.
• the pH of the slurry may be adjusted to a pH value in the range of about 2.5 to about 5, or about 3.5 to about 5, or of about 2.5 to about 3.5.
• the heavy metals, such as Cd, contained in the calcium- containing solid side stream material will not dissolve into the solution but will remain in the residual solids.
• the amount of potentially harmful contaminants, such as heavy metals, in the solution and any resulting products obtainable from the solution may be kept low.
• the calcium-containing solid side stream material may dissolve relatively efficiently, but the amount of potentially harmful contaminants, such as heavy metals, remains relatively low.
• the pH may however also be optimized such that the consumption of the acid remains economical.
• the temperature of the slurry may be adjusted to improve the rate (reaction kinetics) and/or extent of the reaction of the calcium-containing solid side stream material with the acid.
• the temperature of the slurry may be adjusted to at least 50 °C.
• the rate of the reaction may be particularly increased.
• the slurry may be subjected to mixing in order to improve the rate (reaction kinetics) and/or extent of the reaction of the calcium-containing solid side stream material with the acid.
• This may be done e.g. in a suitable mixing apparatus, for example in a mixing tank.
• Suitable mixers for this purpose may be e.g. a blade mixer comprising a dispersion blade, a high shear impeller, or a rotor-stator mixer.
• the mixing and the formation of the solution may be particularly efficient, if a high shear mixer is used.
• the calcium-containing solid side stream material in a dry or slurried form is mixed with the acid by feeding them (i.e. both the calcium-containing solid side stream material and the acid) to a zone of high shear forces within a high shear mixer and subjected simultaneously to the zone of high shear forces.
• the calcium-containing solid side stream material is treated with the acid and the solution comprising the calcium and/or magnesium salt of the acid is formed at least partially in the high shear mixer.
• the calcium- containing solid side stream material and the acid, or the slurry are fed to and subjected to the zone of the high shear forces, these forces may be exerted to substantially the entire volume of the calcium- containing solid side stream material and acid.
• blade mixers may produce high shear forces at the rim of the blade, but they do not form a zone of high shear forces, through which all or essentially all of the calcium-containing solid side stream material and acid would be forced.
• high shear mixers such as impact mixers (e.g.
• Atrex- type mixers may produce high shear forces and all or essentially all of the calcium-containing solid side stream material and the acid, due to the geometry of the mixer, is forced through the zone of high shear forces formed by the rotors. For example, at least about 90 w-%, or at least about 95 w-%, or at least about 99 w-% of the calcium-containing solid side stream material and acid or the slurry may pass through the zone of high shear forces.
• the calcium-containing solid side stream material and the acid are therefore efficiently mixed, and the mixing may be faster than e.g. using a conventional mixer, i.e. the residence time through the high shear mixer may be reduced. Energy consumption may also be reduced. Furthermore, it may be possible to use an acid of a higher concentration and/or a slurry with a higher solids content than when using another type of mixer, such as a conventional blade mixer.
• the energy intensity of the high shear forces to which the calcium-containing solid side stream material and the acid, or the slurry, are subjected in the high shear mixer may be selected depending on various factors.
• the energy intensity may be such that the calcium-containing solid side stream material is efficiently slurried with the acid.
• the energy intensity may therefore be, for example, at least 400 kWh/m 3 .
• Any energy intensities described in this specification may be calculated on the basis of the volume occupied by the calcium-containing solid side stream material and the acid and/or the slurry fed into the high shear zone.
• the residence time of the calcium-containing solid side stream material and the acid and/or of the slurry in the zone of high shear forces may be about 0.01 to 60 seconds, or longer, if desired.
• the high shear mixer may be capable of operating continuously.
• the zone of high shear forces is formed by a mixing zone of a high shear mixer having at least one rotating rotor element.
• the zone of high shear forces is formed by a mixing zone of a high shear mixer having at least one static stator element and at least one rotating rotor element.
• the zone of high shear forces is formed by a mixing zone of a high shear mixer having at least two counter-rotating rotors.
• a high shear mixer may be an impact mixer, for example an impact mixer sold under the trade name Atrex® (Megatrex Oy) .
• Such a high shear mixer may comprise a first rotor provided with blades and a second rotor provided with blades, wherein the first and second rotor are arranged concentrically with each other and configured to rotate to opposite directions in relation to each other, and the calcium- containing solid side stream material and the acid and/or the slurry are supplied through the rotors such that they are repeatedly subjected to shear forces by the effect of the blades, the effect of the blades thereby forming the zone of high shear forces and mixing the calcium-containing solid side stream material and the acid.
• the rotor elements may be capable of rotating at a speed of about 500 to 5000 rpm.
• a high shear mixer are described e.g. in WO 2013/072559 (page 7, line 1 - page 11, line 17 and Figures 1-4) or in FI 105112 B (e.g. the apparatus described in Figs. 1 - 5 and associated paragraphs in the text, e.g. p. 5, 1. 30 to p. 8, 1. 31) , which are herein incorporated by reference in their entirety.
• Such a Cavitron-type high-shear mixer may comprise a dispersing unit or shock-wave reactor. In the dispersing unit or shock-wave reactor, a zone of high shear forces is induced by a rotor/stator system having passage gaps at the rotor and stator.
• the Cavitron-type high-shear mixer may be configured to fill the gaps arranged in a row with the calcium- containing solid side stream material and the acid or the slurry, such that they are/it is centrifugally accelerated by the rotor to gaps in an adjacent row of gaps, thereby generating alternating pressure fields. Examples of possible high shear mixers may be described e.g. in US3165299A and US3589363.
• the method may further comprise separating the solution obtained from residual solids. This can be done, for example, by filtering or using centrifugal forces.
• the residual solids are separated using at least one of a decanter centrifuge or a pressure filter.
• the pressure filter may be a vertical pressure filter. A vertical pressure filter may have a relatively good performance for separating the residual solids. However, the pressure filter may also be a horizontal pressure filter; other filter types may also be contemplated.
• the residual solids may further be treated by washing them with acid. The acid used in the washing may be the same acid used in the treatment, or it may be selected independently. The acid washing may further dissolve the residual solids.
• the solution and optionally also the residual solids may then be recovered.
• the solution may be utilized for various purposes, either as such or after further treatment.
• the method may further comprise concentrating the solution prior to use and/or further treatment.
• the method may further comprise using the solution as a nutrient solution in biological waste water treatment.
• the solution comprising the calcium and/or magnesium salt of the acid may be conveyed to a waste water treatment plant for use as a nutrient solution in biological waste water treatment within the waste water treatment plant. This may allow nutrients obtainable from the green liquor dregs of a chemical pulping plant to be reused at the waste water treatment plant of the same chemical pulping plant and may thus be logistically beneficial.
• the nutrient solution can be conveyed and used as such, or after being concentrated, there may not be any need to further treat the solution prior to using it in the biological waste water treatment.
• Microorganisms, such as bacteria, used in the biological waste water treatment can utilize components of the solution as nutrients.
• the pH of the solution may be adjusted prior to using it as the nutrient solution, if desired. It may also be possible to purify the solution from certain harmful components prior to using it as the nutrient solution, if desired.
• the method may further comprise treating the solution by electrolytical water treatment, thereby removing at least a portion of harmful substances, such as heavy metals, contained in the solution.
• composition of the solution and also of the salt(s) of the acid may, at least to some extent, depend on the composition of the calcium- containing solid side stream material, it may be possible to separate the calcium and/or magnesium salt from the solution either together or separately.
• the method may comprise precipitating and/or crystallizing the calcium and/or magnesium salt of the acid contained in the solution from the solution.
• the calcium and/or magnesium salt thus obtainable may be used for various purposes, for example for fertilizing and/or soil conditioning.
• the precipitating and/or crystallizing may be done by evaporating the water in the solution.
• the method may further comprise drying and/or flaking the product thereby obtainable comprising the calcium and/or magnesium salt of the acid precipitated and/or crystallized from the solution.
• the yield of the calcium and/or magnesium salt of the acid may be e.g. at least about 70 % (w/w) , or at least about 80 % (w/w) , or at least about 85 % (w/w), of the calcium and/or magnesium contained in the calcium-containing solid side stream material, but may depend e.g. on the type of the calcium- containing solid side stream material, the amount of the acid and other factors.
• the residual solids may be discarded, for example by disposing of them in a landfill. It may also be possible to treat them further to reduce the amount of harmful substances in them. It may also be possible to utilize or reuse them further.
• the treatment with an acid may be repeated after the first treatment, i.e. treating the calcium-containing solid side stream material with the acid.
• the residual solids may be further treated with an acid (the same or a different acid, which may be selected independently from the acid used to treat the calcium-containing solid side stream material in the first treatment) , thereby obtaining a second solution comprising a calcium and/or magnesium salt of the acid.
• the second solution may be combined with the solution obtained in the first treatment, or the solutions may be used and/or treated further separately.
• a solution comprising a calcium and/or magnesium salt is also disclosed. The solution may obtainable by the method according to one or more embodiments described in this specification.
• the calcium and/or magnesium salt may be any calcium and/or magnesium salt of the acid described in this specification.
• the solution may be used for various purposes, such as for fertilizing or soil conditioning.
• nitrate salts of calcium and optionally of magnesium and/or sodium may be useful and well suited for fertilizing purposes.
• a product comprising the calcium and/or magnesium salt of the acid precipitated and/or crystallized from the solution obtainable by the method according to one or more embodiments described in this specification is also disclosed.
• the product may be used for various purposes, such as for fertilizing or soil conditioning.
• the product may be, for example, a fertilizer product or a soil conditioner.
• the product may be or comprise the dried calcium and/or magnesium salt of the acid.
• the product may further comprise other salts, for example sodium (Na) salts of the acid, and possibly also other calcium, magnesium and/or sodium salts.
• the product may be a solid product.
• the cadmium (Cd) content of the product and/or of the solution may be less than or equal to 3 mg/kg, or less than or equal to 2.5 mg/kg, or less than or equal to 2 mg/kg, or less than or equal to 1.5 mg/kg, based on the total dry weight of the product or solution .
• a system for the treatment of calcium- containing solid side stream material obtainable from a chemical recovery process of a chemical pulping process is disclosed.
• the system may comprise
• a separation apparatus for separating the solution comprising the calcium and/or magnesium salt of the acid from residual solids.
• the apparatus for mixing the calcium- containing solid side stream material with an acid to form a solution comprising a calcium and/or magnesium salt of the acid may comprise or be a high shear mixer.
• the high shear mixer comprises a first rotor provided with blades and a second rotor provided with blades, wherein the first and second rotor are arranged concentrically with each other and configured to rotate to opposite directions in relation to each other, so that the calcium- containing solid side stream material and the acid or the slurry thereof are repeatedly subjected to shear forces by the effect of the blades, the effect of the blades thereby mixing the calcium-containing solid side stream material and the acid.
• a high shear mixer is thus configured to form the zone of high shear forces by the effect of the blades.
• the high shear mixer is a Cavitron-type mixer.
• the system may further comprise a pressure filtration unit for filtering the calcium-containing solid side stream material prior to mixing it with the acid, i.e. a pressure filtration unit configured to filter the calcium-containing solid side stream material prior to mixing it with the acid.
• the calcium-containing solid side stream material may be any calcium-containing solid side stream material described in this specification, for example green liquor dregs.
• the pressure filtration unit may be a vertical pressure filtration unit.
• the separation apparatus i.e. the separation apparatus configured to separate the solution comprising the calcium and/or magnesium salt of the acid from residual solids, may be, for example, a filtration apparatus, a centrifugation apparatus, a decantation apparatus, a clarification apparatus, a flotation apparatus or a sedimentation apparatus.
• the separation apparatus is a pressure filter, such as a vertical pressure filter or a horizontal pressure filter.
• the system may also comprise e.g. an evaporation apparatus for evaporating water from the solution comprising the calcium and/or magnesium salt of the acid, i.e. configured to evaporate water from the solution comprising the calcium and/or magnesium salt of the acid.
• the system may further comprise an apparatus for drying, i.e. configured to dry; an apparatus for crystallizing, i.e. configured to crystallize; and/or an apparatus for flaking, i.e. configured to flake, the product comprising the calcium and/or magnesium salt of the acid.
• the system may further comprise a waste water treatment plant.
• the system may further comprise a chemical pulping plant and a waste water treatment plant for treating waste water obtainable from the chemical pulping plant, i.e. configured to treat waste water obtainable from the chemical pulping plant.
• the system may further comprise a flow connection, e.g. a conduit or piping, for conveying the solution comprising the calcium and/or magnesium salt of the acid to the waste water treatment plant for use as a nutrient solution in biological waste water treatment within the waste water treatment plant (i.e. configured to convey the solution to the waste water treatment plant) .
• a flow connection e.g. a conduit or piping
• Fig. 1 illustrates a method and a system 14 for the treatment of a calcium-containing solid side stream material 1.
• the calcium-containing solid side stream material 1 may be obtainable from a chemical pulping process 3, and specifically from the chemical recovery process 2 of the chemical pulping process 3 of a chemical pulping plant.
• the calcium- containing solid side stream material 1 may be green liquor dregs obtainable by clarifying green liquor, e.g. using a suitable clarifier.
• green liquor dregs are depicted in this exemplary method and system, other calcium-containing solid side stream materials may also be obtainable from the chemical recovery process 2 of the chemical pulping process 3.
• the system 14 may therefore comprise e.g.
• the system comprises a chemical recovery system.
• the chemical recovery system may comprise e.g. a soda recovery unit, a lime slaking unit, a lime sludge reburning kiln, and/or an apparatus purification of flue gas from lime sludge reburning, such as an electrostatic precipitator.
• the chemical recovery system may further comprise a clarifier for clarifying green liquor; green liquor dregs 1 may be obtainable from the clarifier.
• the green liquor dregs 1 may be filtered using a suitable filter, for example a pressure filter 6.
• the pressure filter 6 may be a vertical pressure filter, but could also be a horizontal pressure filter.
• the filtering concentrates the green liquor dregs 1. It may also allow returning more sodium back to the circulation of chemicals of the process.
• the green liquor dregs 1 may also be filtered using a filter, for example a rotary drum vacuum filter 18.
• the filter is precoated with lime mud.
• the green liquor dregs cake thereby obtained will then comprise both the green liquor dregs and lime mud, for example at a ratio of 1:1.
• the lime mud may typically comprise mainly CaCO 3 .
• This type of green liquor dregs 1 may be referred to as GLD to landfill.
• Either type of green liquor dregs 1 obtained as a cake may be preground, i.e. comminuted, so that its surface area increases. This can be done using a suitable grinding apparatus 19, such as a mill. However, in many embodiments, pregrinding may not be necessary. The grinding apparatus 19 and the pregrinding are therefore fully optional.
• the green liquor dregs 1, or any other calcium-containing solid side stream material, either dry or in a slurried form, may be premixed with an acid 4 and optionally with water using a suitable mixing apparatus 20, for example a mixer or a mixing tank.
• a suitable mixing apparatus 20 for example a mixer or a mixing tank.
• Such a mixer may be e.g. a simple blade mixer.
• a slurry 7 may thus be obtained.
• the premixing is not necessary, but instead the green liquor dregs 1 and the acid 4 may be fed directly and separately to an apparatus 9 for mixing the calcium-containing solid side stream material (in this embodiment, green liquor dregs) with the acid 4 to form a solution 5 comprising a calcium and/or magnesium salt of the acid. In the apparatus 9 they are then mixed, thereby forming a slurry 7.
• the apparatus 9 is a high shear mixer, there may be no need for the premixing.
• the calcium-containing solid side stream material e.g. green liquor dregs 1
• a solution 5 comprising the calcium and/or magnesium salt of the acid will be formed.
• the required reaction time may depend on various factors, for example the composition of the calcium-containing solid side stream material 1, the concentration and amount of the acid 4, the intensity of the mixing, and/or the pH of the slurry 7.
• the pH of the slurry 7 may be adjusted to a desired value.
• the apparatus 9 for mixing the calcium-containing solid side stream material 1 with the acid 4 to form the solution 5 comprising a calcium and/or magnesium salt of the acid is a high shear mixer.
• the high shear mixer 9 may be configured to form a zone 8 of high shear forces within the high shear mixer and to subject the calcium-containing solid side stream material 1 and the acid 4, or the slurry 7, simultaneously to the zone 8 of high shear forces, thereby mixing them.
• An embodiment of such a high shear mixer is described in detail in Figs. 2A and 2B.
• any mixer, in particular any high shear mixer (for example, a Cavitron-type mixer) described in this specification could be contemplated instead. All or essentially all of the calcium-containing solid side stream material 1 and the acid 4 and/or the slurry 7 may pass through the zone 8 of high shear forces, such that all or essentially all of them are subjected to the high shear forces.
• the resulting solution 5 and residual solids 10 may be conveyed to and separated using a separation apparatus 15 for separating the solution 5 comprising the calcium and/or magnesium salt of the acid from the residual solids 10.
• the separation apparatus 15 may comprise or be e.g. a filtration apparatus, a centrifugation apparatus, a decantation apparatus, a clarification apparatus, a flotation apparatus or a sedimentation apparatus.
• the filtering apparatus may, in an embodiment, be a pressure filter, e.g. a vertical pressure filter or a horizontal pressure filter.
• the solution 5, or at least a portion thereof, obtained may be treated further.
• the system 14 may comprise an electrolytical water treatment apparatus 12 for removing at least a portion of harmful substances, such as heavy metals, contained in the solution.
• an electrolytical water treatment apparatus 12 for removing at least a portion of harmful substances, such as heavy metals, contained in the solution.
• the electrolytical water treatment is, in many embodiments, not necessary.
• Other suitable apparatuses for removing at least a portion of harmful substances may also be contemplated, for example an ion exchange apparatus.
• the system 14 may also comprise e.g. an evaporation apparatus 21 for evaporating water from the solution comprising the calcium and/or magnesium salt of the acid.
• the evaporation apparatus 21 may be used for precipitating and/or crystallizing the calcium and/or magnesium salt of the acid and any other salts present in the solution 5; other crystallizing appa- ratuses may also be contemplated.
• the system 14 may further comprise an apparatus 22 for drying; and/or an apparatus 23 for flaking the calcium and/or magnesium salt of the acid.
• a product 13 comprising the calcium and/or magnesium salt of the acid precipitated and/or crystallized from the solution 5 may thus be obtained.
• Additives or other substances may be added to the product 13, if desired.
• additives may include e.g. additives for assisting with forming granules of the product, coatings, or components for improving the nutritional content of the product.
• nitrogen-containing compounds such as nitrogen salts or urea may be added to increase the nitrogen content of the product; ash; one or more of other nutrients, such as one or more of phosphorus, potassium, calcium, magnesium, sulphur, boron, chlorine, manganese, iron, zinc, copper, cobalt, molybdenum, nickel, silicon, selenium or sodium, or other components of a fertilizer or soil conditioner.
• the product may thus comprise other components, for example any of the components described above.
• the system 14 may comprise a waste water treatment plant 17 and a biological waste water treatment system 11 therein.
• the solution 5, or at least a portion of the solution 5, may be conveyed to a waste water treatment plant 17.
• the system 14 may therefore comprise a flow connection 16, for example a suitable conduit or piping, for conveying the solution comprising the calcium and/or magnesium salt of the acid to the waste water treatment plant 17 for use as a nutrient solution in biological waste water treatment 11 within the waste water treatment plant.
• the solution 5 may be added to the biological waste water treatment process, for example to a biological purification process, in which the microbes, e.g. bacteria, may utilize the calcium and/or magnesium salt of the acid and optionally any other components in the solution 5 as nutrients.
• the solution 5 obtainable from the electrolytical water treatment apparatus 12, i.e. the solution 5 treated by electrolytical water treatment may also be conveyed to the waste water treatment plant 17.
• the system 14 may further comprise conduits or flow connections, for example pipings, between the parts of the system for conveying the calcium- containing solid side stream material 1; the acid 4; the slurry 7; the solution 5; the residual solids 10; and/or the product 13.
• conduits or flow connections for example pipings, between the parts of the system for conveying the calcium- containing solid side stream material 1; the acid 4; the slurry 7; the solution 5; the residual solids 10; and/or the product 13.
• Fig. 2A illustrates a cross-sectional side view of an exemplary high shear mixer 9 which can be used for mixing the calcium-containing solid side stream material 1 and the acid 4.
• Fig. 2B shows the same exemplary high shear mixer 9 as a cross-sectional top view.
• This embodiment of the high shear mixer 9 is merely an example, and it is clear to a skilled person that various other high shear mixers or other mixers may be utilized for the same purpose and that their structures and operations may differ from the one described herein.
• the high shear mixer 9 described in these Figs is similar e.g to Atrex CD 500 G45 which is suitable for the method.
• the high shear mixer 9 comprises a first rotor 24 and a second rotor 25 arranged concentrically within each other such that they are configured to rotate around a common rotation axis 26.
• the first rotor 24 and the second rotor 25 are configured to rotate to opposite directions in relation to each other.
• the first and second rotor 24, 25 thus form a pair of counter-rotating rotors.
• the high shear mixer 9 may comprise two, three or more rotors.
• one of the first or second rotors 24, 25 could be replaced by a stator.
• solutions comprising at least two counter-rotating rotors may be more efficient at causing high shear forces .
• the rotors 24, 25 are provided with blades or ribs 33.
• the blades 33 are arranged in at least two concentric rims 27, 28, 29, 30, 31, 32.
• the blades 33, connected to the rotors 24, 25, are thus also configured to rotate around the common rotation axis 26.
• the at least two concentric rims are configured to rotate to opposite directions in relation to each other.
• the exemplary embodiment of the high shear mixer 9 shown in Figs. 2A and 2B comprises blades arranged in a plurality of rims 27, 28, 29, 30, 31, 32 - specifically six in this embodiment.
• the blades 33 of three of the rims 27, 29, 31 are configured to rotate in the same direction.
• the blades of the other three rims 28, 30, 32 are configured to rotate in the opposite direction.
• the rims 27, 28, 29, 30, 31, 32 are arranged pairwise such that one rim is always followed and/or preceded in the radial direction by a rim of counter-rotating blades.
• the rotors may be capable of rotating at a speed of about 500 to 5000 rpm, but speeds lower than about 500 or greater than about 5000 may also be contemplated.
• the blades 33 may be elongated pieces, the height of which may be greater than their width (i.e. their dimension in the radial direction of the rotors) .
• Figs. 2A and 2B show measurements of certain dimensions of the exemplary high shear mixer 9 in millimetres, but various geometries and dimensions for the rotors and the blades may be contemplated.
• the blades 33 are parallel to the radial direction, but at least some of the blades 33, for example those arranged in the outermost rim 32 or in the two outermost rims 31, 32, may be arranged at an angle to the radial direction.
• the blades 33 and optionally other parts of the rims and rotors may be formed of an acid compatible alloy.
• the high shear mixer 9 comprises a housing 34 within which the rotors 24, 25 may be arranged.
• the high shear mixer 9 further comprises an inlet 35 for feeding in the calcium-containing solid side stream material 1 and the acid and/or the slurry 7.
• the inlet 35 opens to the innermost rim 27.
• the high shear mixer 9 further comprises an outlet 36 for removing the slurry 7.
• the outlet 36 opens to the outermost rim 32 and extends through the housing 34.
• the rotors 24, 25 can be considered to be flow-through rotors, such that the calcium-containing solid side stream material 1 and the acid and/or the slurry 7 may pass through the rotors via gaps between the blades 33 extending in the direction of the rotation axis 26 and therefore also through the zone 8 of the high shear forces.
• the calcium-containing solid side stream material 1 and the acid and/or the slurry 7 may pass through the zone 8 of high shear forces in a given residence time.
• the calcium-containing solid side stream material 1 and the acid 4 and/or the slurry 7 may thus be supplied outwards in the radial direction with respect to the rotation axis 26 of the rotors 24, 25 such that the calcium-containing solid side stream material 1 and the acid and/or the slurry 7 are repeatedly subjected to shearing and impacting forces by the effect of the blades 33 of the counter-rotating rotors.
• the blades 33 provide collision surfaces for impacting.
• the zone 8 of high shearing forces is thus generated in the space along which the blades move upon the rotation of the rotors.
• the extent of the zone 8 of high shearing forces is shown in Fig. 2A in the direction of the rotation axis 26 and in Fig. 2B in the radial direction.
• the calcium-containing solid side stream material 1 and the acid or the slurry 7 may thus be supplied through the rotors 24, 25 such that they are repeatedly subjected to shear forces by the effect of the blades 33, the effect of the blades 33 thereby forming the zone 8 of high shear forces and mixing the calcium-containing solid side stream material 1 with the acid 4 intimately.
• the rotary movement of the blades 33 produce narrow gaps 37 between the blades 33, in which the calcium-containing solid side stream material 1 and the acid and/or the slurry 7 are subjected to shear forces.
• the direction of the impacts caused by the blades 33 changes at a high frequency.
• the calcium-containing solid side stream material and the acid are therefore repeatedly impacted by and subjected to the shearing forces caused by the blades 33. These impacting forces and shearing forces therefore cause the mixing of the calcium-containing solid side stream material and the acid, and may also cause the calcium-containing solid side stream material to be ground to smaller particles.
• the calcium-containing solid side stream material 1 and the acid 4 and/or the slurry 7 fed into the zone 8 of high shear forces thus can occupy a volume within the rims, i.e. the space along which the blades 33 move upon the rotation of the rotors and which is not occupied by the blades or other parts of the rotors.
• Various parameters such as the number of the rotors and rims, the number and/or density of the blades in each rim and/or rotor, the geometry (e.g. angles) of the blades and/or the rotation speeds of the rotors may be used to affect the shear forces and the energy intensity to which the calcium-containing solid side stream material and the acid and/or the slurry are subjected.
• the energy intensity in the zone 8 of high shear forces may be calculated or estimated by dividing the input power of the high shear mixer by the volume of the calcium-containing solid side stream material 1 and the acid 4 and/or the slurry 7 fed into the zone 8 of high shear forces.
• the residence time of the calcium-containing solid side stream material and the acid and/or the slurry in the zone 8 of high shear forces may be about 0.01 to 60 seconds, or longer, if desired.
• the type of high shear mixer described in these Figs, may however be quite efficient, and residence times of a few seconds may in many cases suffice.
• Green liquor dregs were obtained from a pulp mill and treated with a vacuum drum filter. Lime mud was used as a precoat. This treated fraction was referred to as green liquor dregs to landfill. Based on four separate measurements, the calcium content of the lime mud had been 163-430 g/kg ds measured by ICP-OES. Green liquor dregs to filter was the fraction entering the vacuum filter without any lime mud. The green liquor dregs, water and acid were mixed. After a reasonable mixing time, the solution was filtrated with a Buchner filter, as the soluble salts remained in the filtrate. The cake and the fil- trate were separated and dried overnight at 105 °C.
• Ion chromatography or ion-exchange chromatography
• ICP-OES inductively coupled plasma optical emission spectrometry
• EDS Energy Dispersive X- ray Spectroscopy
• FTIR Fourier Transform Infrared Spectrometer
• Green liquor dregs (GLD to landfill) from a pulp mill were mixed with distilled water and nitric acid by a magnetic mixer.
• the trial points are presented in Table 1. Nitric acid with different concen- trations, elevated temperature and different mixing times were tested.
• the sulphate and nitrate contents of the three samples were defined by IC, and the results are presented in Fig. 4.
• the calcium, magnesium and sodium contents of the few samples were measured by ICP.
• the results are presented in Fig. 5. Based on IR spectra obtained (not shown) , the composition of formed salts are likely calcium nitrate, but also magnesium nitrate is present.
• a mechanical mixer was used in the present example.
• the trial points are presented in Table 2. Nitric acid was used and the pH target was near neutral .
• the EDS results of the salts are presented in Fig. 6.
• the formed salts contained mainly calcium. Also magnesium, sodium and sulphur were present.
• the contents of calcium, magnesium, sodium and sulphur were also measured from a few test points by ICP.
• the formed salt was quite pure calcium nitrate, because the contents of magnesium, sodium and sulphur were quite low.
• the other samples also contained mainly calcium as seen in Fig. 7.
• the formed salts were nitrates, mainly calcium nitrates but also magnesium nitrates were found to be present.
• Acetic acid was used to form calcium acetate.
• the raw material of these experiments was green liquor dregs to landfill.
• the trial record is presented in Table 4.
• Green liquor dregs to filter was selected as the raw material for these tests, because the lime mud used as a pre-coat when green liquor dregs to landfill is formed, could be utilized elsewhere due to its heavy metal free composition.
• Nitric acid, phosphoric acid and acetic acid were used in these trials.
• the trial record of these tests is presented in Table 6.
• salts were mainly sodium salts.
• Nitric acid formed sodium nitrate
• phosphoric acid formed sodium phosphate
• acetic acid formed sodium acetate.
• the vertical Larox pressure filter was tested in order to see if bigger cakes could be obtained.
• the raw material was green liquor dregs to filter from a pulp mill. Three chambers were used in the filter.
• the Larox filtrated green liquor dregs to filter were acidified with nitric acid to form calcium nitrate and with acetic acid to form calcium acetates. The performed trials and results are presented below.
• the Larox filtered green liquor dregs to filter was treated with nitric acid to form calcium nitrate .
• the filtrate was analysed as such without any drying procedures.
• the ICP measurements of the salt liquids are presented in Fig. 11.
• the amount of calcium was similar in all test points. Quite some sodium, magnesium and sulphur were also present.
• the salts were likely to be nitrate salts containing calcium ni- trate but possibly also sodium and magnesium nitrates.
• the formed salts were nitrates, mainly calcium nitrates but also magnesium nitrates. Based on the IC analysis, the major part of the ions are nitrates and there was only very little of sulphates. Based on the ICP measurements, approximately half of the analysed elements were calcium, but also quite some magnesium and sodium were present.
• Acetic acid trial points The Larox filtered green liquor dregs to filter was treated with acetic acid to form calcium acetate.
• the trial procedure was similar to the nitric acid experiments, only the acid grade and the amount of acid were changed.
• the trial record is presented in Table 12.
• the raw material of the trial point 11 was Larox filtrated green liquor dregs to filter without wash stage and the raw material of the trial point 14 was Larox filtrated and washed green liquor dregs to filter.
• the results of the ICP analysis are presented in Fig. 13. Most of the salts were made of calcium, but there was also quite a lot sodium, magnesium and sulphur in the filtrate.
• the results of the EDS analyses are presented in Figs. 14A and 14B.
• IC results are presented in Fig. 15. A major part of the ions were acetate ions and there were also very small amounts of sulphates and nitrates.
• the embodiments described hereinbefore may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment.
• a method, a product, a system, or a use, disclosed herein, may comprise at least one of the embodiments described hereinbefore. It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item refers to one or more of those items.
• the term "comprising" is used in this specification to mean including the feature (s) or act(s) followed thereafter, without excluding the presence of one or more additional features or acts.

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