CN110818048A - Polysilicate iron/cationic starch composite flocculant and preparation method thereof - Google Patents
Polysilicate iron/cationic starch composite flocculant and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a polysilicate iron/cationic starch composite flocculant and a preparation method thereof. The method has simple process and low cost, changes the titanium white waste acid into valuable, treats the pollution of the culture wastewater, realizes the treatment of waste by waste, and opens up a new way for the resource utilization of the titanium white waste acid.
Description
Technical Field
The invention belongs to the technical field of composite materials, and particularly relates to a polysilicate-ferric/cationic starch composite flocculant and a preparation method thereof.
Background
In recent years, aquaculture has developed vigorously. A national fishery statistical condition review in 2018 indicates that the economic total value of fishery in the whole society in 2018 is 25864.47 hundred million yuan, the fishery output value is 12815.41 hundred million yuan, and the output value ratio of the cultured products to the harvested products is 77.8: 22.2. During the aquaculture process, a large amount of waste is accumulated at the bottom of the pond. The wastes mainly come from residual bait thrown in the cultivation, excrement of fishes and shrimps and the like. In modern aquaculture, fish can generally absorb about 25% of protein value of the added feed, and most of the rest of the feed enters a water body. Organic matters in the feed are gradually converted into nitrite nitrogen and finally converted into nitrate nitrogen in an oxygen-enriched environment on the upper layer of the water body; in the anoxic environment of the water body, organic matters are gradually converted into ammonia nitrogen and nitrogen. The fish drug added in the feed can be slowly enriched in the water body. In such an environment, the oxygen content of the water body is reduced, the normal growth of the fishes and shrimps can be influenced by the suspension of the residual feed particles in the water, and the eutrophication of the water body is easily caused by a large amount of nutrient salts. Therefore, it has important significance to explore a simple and feasible cultivation wastewater treatment technology with low cost.
The flocculation sedimentation method is to add a flocculating agent into the water body, and flocculate the particles in the water body by utilizing the generated flocs so that the particles are gathered and then settled to the bottom of the water. The flocculation sedimentation method for treating sewage has the advantages of simple operation, convenient use and wide application range, and is widely applied to wastewater treatment, so that the dosage of the flocculating agent is extremely large and is increased by a very high percentage every year. Traditional flocculants have been gradually replaced by inorganic and organic polymeric flocculants. The inorganic polymeric flocculant (polymeric iron and polymeric aluminum) has better effect than the traditional flocculant (low molecular iron salt and aluminum salt) and lower price than the organic polymeric flocculant, but the relative molecular mass and granularity and the flocculation bridging capability of the inorganic polymeric flocculant are lower than those of the organic polymeric flocculant, and simultaneously, the problem of instability of further hydrolysis reaction exists. The organic polymer flocculant mainly comprises two types of artificial synthesis and natural modification, wherein the artificial synthesized organic polymer flocculant such as polyacrylamide, polyethyleneimine and the like has the characteristics of small using amount, high coagulation speed, large and tough flocculating body in use, is widely applied to sewage treatment, but has higher price and toxicity if unpolymerized monomers are left during production; the natural modified polymeric flocculant has the characteristics of wide raw material source, low price, easy biodegradation and the like, and particularly attracts attention. In the market of foreign water treatment agents, the starch modified flocculant occupies a large market proportion, and the development and application research is active. However, the natural polymeric flocculant has a low charge density and a low molecular weight, and is easily biodegradable and loses activity, and these weaknesses promote research and development towards various composite polymeric flocculants.
The aquaculture wastewater is a complex and stable dispersion system, and a single flocculating agent cannot achieve a satisfactory treatment effect, so researchers begin to develop the composite flocculating agent in recent years. Practice proves that the composite flocculant has better effect than a single flocculant and better flocculation effect of an inorganic/organic composite flocculant, and is expected to become a new generation of high-efficiency flocculant. The compounding mechanism of the inorganic/organic composite flocculant is mainly related to the synergistic effect of the inorganic/organic composite flocculant, and on one hand, sewage impurities are adsorbed by the inorganic flocculant and are coagulated by the electric neutralization; on the other hand, the organic polymer is adsorbed on the active groups of the organic polymer through the bridging action of the organic polymer, so that other impurity particles are captured and precipitated together, and a more excellent flocculation effect is achieved, namely the result of the combined synergistic effect of the high positive charge density of the inorganic flocculant and the capturing function of the organic polymer flocculant.
The titanium dioxide powder storage method has the advantages that titanium ore storage is abundant in China, the storage amount is at the top of the world, and the titanium dioxide powder industry is developed vigorously with the continuous improvement of the industrial level of China. More than 98 percent of titanium dioxide in China is produced by a sulfuric acid method, and on average, 6 to 8 tons of waste acid (the mass concentration of sulfuric acid is about 20 percent) and 2.5 to 4 tons of byproduct ferrous sulfate heptahydrate (copperas, FeSO) are generated when 1 ton of titanium dioxide is produced4·7H2O), according to a rough estimate, at least 170 million tons of waste acid and 100 million tons of by-product ferrous sulfate are produced per year by national titanium dioxide plants. The treatment of the waste acid of the visible titanium white becomes a difficult problem for titanium white enterprises in China, and the treatment cost is too high, so that the treatment cost is increasedThe operation cost of titanium dioxide production enterprises is needed to be explored, so that a low-cost treatment method of titanium dioxide waste acid is needed to be explored, the titanium dioxide waste acid and starch are used as raw materials to develop a novel organic-inorganic composite flocculant for treating aquaculture wastewater, the purpose of treating the titanium dioxide waste acid is achieved, the purpose of treating the aquaculture wastewater is also achieved, and good economic benefits and environmental benefits are brought to social development.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a polysilicate iron/cationic starch composite flocculant and a preparation method thereof.
The technical scheme of the invention is as follows:
the ferric polysilicate/cationic starch composite flocculant comprises the following raw materials: the titanium dioxide waste acid, cationic starch, a sodium silicate solution, lime milk, hydrogen peroxide and alkali, wherein the molar ratio of silicon in the sodium silicate solution to iron in the titanium dioxide waste acid is 1:3-5, and the mass ratio of the iron in the titanium dioxide waste acid to the cationic starch is 1: 0.5-2.
Preferably, the molar ratio of silicon in the sodium silicate solution to iron in the titanium white waste acid is 1:4, and the mass ratio of iron in the titanium white waste acid to cationic starch is 1: 1.5.
Preferably, the total iron concentration of the titanium white waste acid is 1.0-2.0 mol/L, and the density is 1.6-1.9 g/mL.
Preferably, in the technical scheme, the alkali is a sodium hydroxide solution, the lime milk is a slurry obtained by dissolving calcium oxide in water, and the sodium silicate solution is a solution obtained by dissolving sodium silicate in water.
The preparation method of the polysilicate-iron/cationic starch composite flocculant comprises the following steps:
(1) waste acid neutralization: adding lime milk into the titanium white waste acid, continuously stirring, and neutralizing until the pH value is 0.5-1.5 to obtain a mixture;
(2) and (3) suction filtration: performing suction filtration on the mixture to obtain filtrate which is neutralized waste acid for later use;
(3) curing polymerization: adding a sodium silicate solution into the neutralized waste acid, uniformly stirring, then adding hydrogen peroxide to oxidize ferrous iron in the solution into ferric iron, then adding an alkali to adjust the pH value of the solution to 2.5-3.0, then adding cationic starch, uniformly stirring, continuously adding the alkali to adjust the pH value of the solution to 3.5-4.0, standing for 1-3h to carry out curing polymerization reaction, thus obtaining the polysilicate iron/cationic starch composite flocculant.
Preferably, in the step (3), the molar ratio of the added hydrogen peroxide to the ferrous iron in the solution is 1-1.5: 2.
Because the sulfuric acid content of the titanium white waste acid is higher, a certain amount of lime milk is added for neutralization, so that the pH value of the titanium white waste acid can be increased, the alkali consumption is saved for the subsequent process, and the sulfate radical can be recovered to prepare the white gypsum.
Ion reaction formula 2H for reducing ferrous ions by hydrogen peroxide++2Fe2++H2O2→2Fe3++2H2O shows that when the molar ratio of the added amount of the hydrogen peroxide to the ferrous iron in the solution is 1:2, the ferrous iron in the solution can be just oxidized into the ferric iron, so the molar ratio of the added amount of the hydrogen peroxide to the ferrous iron in the solution can be slightly more than 1: 2.
The principle of the invention is as follows:
when the polysilicate iron/cationic starch composite flocculant is used for wastewater treatment, on one hand, sewage impurities are adsorbed by polysilicate iron and are coagulated by electric neutralization; on the other hand, the cationic starch is adsorbed on the quaternary amine group of the cationic starch through the bridging action of the cationic starch, so that other impurity particles are captured and precipitated together, and a more excellent flocculation effect is achieved, namely the result of the combined synergistic effect of the high positive charge density of the ferric polysilicate and the capturing function of the cationic starch.
The invention has the beneficial effects that:
(1) the invention takes titanium dioxide waste acid as raw material, and prepares the polysilicate-ferric/cationic starch composite flocculant by adding sodium silicate solution, lime cream, sodium hydroxide, hydrogen peroxide and cationic starch.
(2) The polysilicate-ferric/cationic starch composite flocculant has good treatment effect on aquaculture wastewater, and the turbidity removal rate of the aquaculture wastewater is over 93.6 percent; the chroma removal rate is more than 93.3 percent, the COD removal rate is more than 49.6 percent, the total nitrogen removal rate is more than 30.3 percent, and the total phosphorus removal rate is more than 85.3 percent. Compared with the polysilicate iron flocculant, the turbidity removal rate of the polysilicate iron/cationic starch composite flocculant for treating the culture wastewater is improved by more than 7.9 percent; the chroma removal rate is improved by more than 5.8 percent, the COD removal rate is improved by more than 9.3 percent, the total nitrogen removal rate is improved by more than 11.3 percent, and the total phosphorus removal rate is improved by more than 18.8 percent. Moreover, the flocculation time of the polysilicate iron/cationic starch composite flocculant is 30min, which is half of the flocculation time of the polysilicate iron flocculant, the flocculating constituent is large, the sedimentation speed is high, and the supernatant fluid is clear. Therefore, the polysilicate iron/cationic starch composite flocculant has a good treatment effect on aquaculture wastewater.
(3) At present, the flocculating agent prepared by using titanium dioxide waste acid is mostly polymerized ferric sulfate, and the preparation of ferric polysilicate is rarely reported. The invention firstly utilizes titanium dioxide waste acid to prepare the polysilicate iron flocculant, and then compounds the polysilicate iron and the cationic starch by a copolymerization method to successfully prepare the polysilicate iron/cationic starch composite flocculant, which has the advantages of small using amount, large alum blossom, quick sedimentation and the like when being used for treating the culture wastewater.
Drawings
Fig. 1 is an XRD pattern of the polysilicate-iron/cationic starch composite flocculant of the present invention;
FIG. 2 is an infrared spectrum of a polysilicate-iron flocculant, a cationic starch and a polysilicate-iron/cationic starch composite flocculant;
FIGS. 3 and 4 are scanning electron micrographs of the polysilicate-ferric/cationic starch composite flocculant, and FIGS. 5 and 6 are scanning electron micrographs of the polysilicate-ferric flocculant;
FIG. 7 is an EDS analysis chart of the polysilicate iron/cationic starch composite flocculant;
fig. 8 is an XPS total spectrum of the polysilicate-iron/cationic starch composite flocculant, fig. 9 is an XPS graph of Fe2p, fig. 10 is an XPS graph of Si2p, and fig. 11 is an XPS graph of O1 s.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but the present invention is not limited to the scope of the present invention.
Preparing raw materials:
the alkali is sodium hydroxide solution; the lime milk is slurry obtained by dissolving 130g of calcium oxide in 300mL of water; the sodium silicate solution is obtained by dissolving sodium silicate in water.
Example 1
A preparation method of a polysilicate iron/cationic starch composite flocculant comprises the following steps:
(1) waste acid neutralization: adding lime milk into 1L of titanium white waste acid with the total iron concentration of 1.5mol/L and the density of 1.8g/mL, continuously stirring, and neutralizing until the pH value is 1.0 to obtain a mixture;
(2) and (3) suction filtration: performing suction filtration on the mixture to obtain filtrate which is neutralized waste acid for later use;
(3) curing polymerization: adding 0.1L of 3.75mol/L sodium silicate solution into the neutralized waste acid (the molar ratio of silicon in the sodium silicate solution to iron in the titanium white waste acid is 1:4), uniformly stirring, then adding 5mL of 30% hydrogen peroxide to oxidize the ferrous iron in the solution into ferric iron, then adding sodium hydroxide to adjust the pH value of the solution to 3.0, then adding 8.4g of cationic starch (the mass ratio of the iron in the titanium white waste acid to the cationic starch is 1:1.5), uniformly stirring, continuously adding sodium hydroxide to adjust the pH value of the solution to 3.5, standing for 2 hours to carry out curing polymerization reaction, and obtaining the ferric polysilicate/cationic starch composite flocculant.
Example 2
A preparation method of a polysilicate iron/cationic starch composite flocculant comprises the following steps:
(1) waste acid neutralization: adding lime milk into 1L of titanium white waste acid with the total iron concentration of 1.7mol/L and the density of 1.8g/mL, continuously stirring, and neutralizing until the pH value is 1.2 to obtain a mixture;
(2) and (3) suction filtration: performing suction filtration on the mixture to obtain filtrate which is neutralized waste acid for later use;
(3) curing polymerization: adding 0.1L of 3.75mol/L sodium silicate solution into the neutralized waste acid (the molar ratio of silicon in the sodium silicate solution to iron in the titanium white waste acid is 1:4), uniformly stirring, then adding 6mL of 30% hydrogen peroxide to oxidize the ferrous iron in the solution into ferric iron, then adding sodium hydroxide to adjust the pH value of the solution to be 2.8, then adding 11.2g of cationic starch (the mass ratio of the iron in the titanium white waste acid to the cationic starch is 1:2), uniformly stirring, continuously adding sodium hydroxide to adjust the pH value of the solution to be 3.6, and standing for 1.5 hours to carry out curing polymerization reaction, thereby obtaining the ferric polysilicate/cationic starch composite flocculant.
Example 3
A preparation method of a polysilicate iron/cationic starch composite flocculant comprises the following steps:
(1) waste acid neutralization: adding lime milk into 1L of titanium white waste acid with the total iron concentration of 2.0mol/L and the density of 1.9g/mL, continuously stirring, and neutralizing until the pH value is 1.5 to obtain a mixture;
(2) and (3) suction filtration: performing suction filtration on the mixture to obtain filtrate which is neutralized waste acid for later use;
(3) curing polymerization: adding 0.1L of 5mol/L sodium silicate solution into the neutralized waste acid (the mol ratio of silicon in the sodium silicate solution to iron in the titanium white waste acid is 1:3), uniformly stirring, then adding 6mL of 30% hydrogen peroxide to oxidize the bivalent iron in the solution into trivalent iron, then adding sodium hydroxide to adjust the pH value of the solution to 2.6, then adding 5.6g of cationic starch (the mass ratio of iron in the titanium white waste acid to the cationic starch is 1:1), uniformly stirring, continuously adding sodium hydroxide to adjust the pH value of the solution to 3.8, and standing for 3 hours to perform curing polymerization reaction to obtain the polysilicate iron/cationic starch composite flocculant.
Example 4
A preparation method of a polysilicate iron/cationic starch composite flocculant comprises the following steps:
(1) waste acid neutralization: adding lime milk into 1L of titanium white waste acid with the total iron concentration of 1.0mol/L and the density of 1.6g/mL, continuously stirring, and neutralizing until the pH value is 0.5 to obtain a mixture;
(2) and (3) suction filtration: performing suction filtration on the mixture to obtain filtrate which is neutralized waste acid for later use;
(3) curing polymerization: adding 0.1L of 3mol/L sodium silicate solution into the neutralized waste acid (the mol ratio of silicon in the sodium silicate solution to iron in the titanium white waste acid is 1:5), uniformly stirring, then adding 7mL of 30% hydrogen peroxide to oxidize the bivalent iron in the solution into trivalent iron, then adding sodium hydroxide to adjust the pH value of the solution to 2.5, then adding 2.8g of cationic starch (the mass ratio of the iron in the titanium white waste acid to the cationic starch is 1:0.5), uniformly stirring, continuously adding sodium hydroxide to adjust the pH value of the solution to 4.0, standing for 1h to perform curing polymerization reaction, and obtaining the polysilicate iron/cationic starch composite flocculant.
First, material characterization of the polysilicate iron/cationic starch composite flocculant:
the polysilicate-ferric/cationic starch composite flocculant prepared in example 1 is frozen and dried in vacuum to obtain dark brown solid, and then material characterization is carried out.
X-ray diffractometer (XRD) analysis
And scanning the composite flocculant by using an X-ray diffractometer, and analyzing the crystal form structure of the composite flocculant. The test conditions were: the working voltage is 40KV, the working current is 40mA, the scanning speed is 5 degrees/min, and the scanning range is 5-80 degrees.
FIG. 1 is an XRD spectrum of the composite flocculant after freeze drying. After being compared with the standard colorimetric card PDF22004, the crystal form substance is found to be sodium sulfate, and Fe is not detected2(SO4)3、Fe(OH)3、SiO2And the crystal forms of other substances, which indicate Fe in the raw materials3+And silicate ions have been successfully polymerized to form an amorphous, amorphous copolymer. Therein is provided withThe combination of a large amount of sodium sulfate from waste acid and sodium ions in sodium hydroxide used for adjusting pH in the preparation process belongs to a normal phenomenon.
2. Fourier Infrared Spectroscopy (FT-IR) analysis
Tabletting with KBr: a small amount of sample is removed, mixed with dry KBr powder in an agate mortar and ground, pressed into a transparent sheet by a tablet machine and placed into a NicoletIS 10 Fourier infrared spectrometer, and the change of sample groups is analyzed. The scanning wavelength range is 4000-500 cm-1。
FIG. 2 is the infrared spectrum of polysilicate iron flocculant, cationic starch and polysilicate iron/cationic starch composite flocculant. At 3450 and 3280cm-1The vicinity of the peak is an absorption peak of-OH, indicating that the material contains a large amount of hydroxyl groups. While the peak position was from 3280 to 3450cm-1The shift indicates that the polysilicate iron and the cationic starch form hydrogen bonds to be bonded together. At 1650cm-1The bending vibration absorption peak of H-O-H shows that crystal water or hydroxyl complex exists in the material. At 1383cm-1The peak of absorption of C-H bond symmetric bending vibration at 1480cm is located on quaternary ammonium salt group-1Is of the formula-N+(CH3)3A vibration absorption peak. These two peaks appear in the spectra of the cationic starch and the composite flocculant, indicating that the starch has been attached to the polysilicate iron flocculant, demonstrating that the composite flocculant has been successfully made. 1150cm-1Is the vibration absorption peak of Si-O, 1016cm-1Is characterized by a C-O-C characteristic stretching vibration absorption peak of starch, 970cm-1Is a characteristic peak of Si-O-Fe at 620cm-1The peak is a characteristic peak of Fe-O. These characteristic peaks demonstrate that silicic acid is polymerized in the polysilicate iron and the composite flocculant, and ferric ions are wrapped in the polysilicate iron and the composite flocculant, and according to the polymerization theory of the silicic acid, the polysilicate iron and the composite flocculant both form Si-O-Fe-O-Si. Fe is not only complexed with silicon but also combined with hydroxyl in the process of coordination and combination to form a hexa-coordination structure. The presence of these characteristic peaks indicates that the composite flocculant has been successfully prepared.
3. Scanning Electron Microscope (SEM) analysis
And smearing a small amount of dry samples on the conductive gel of a scanning electron microscope sample tray, then carrying out gold spraying treatment on the samples, and observing the surface appearance of the samples by using an S-3400 scanning electron microscope.
Fig. 3 to 6 are SEM images of samples, wherein fig. 3 and 4 are SEM images of a polysilicate iron/cationic starch composite flocculant, and fig. 5 and 6 are SEM images of a polysilicate iron flocculant, wherein the magnifications of fig. 3 and 4, fig. 5 and 6 are different. It can be seen that the polysilicate iron flocculating agent is in a crystal cluster block shape as a whole, has a tendency of being bonded together, and has fine scale-like protrusions on the surface, because the polysilicate iron exists in a state that a high molecular polymer is combined with water in water, and when a sample is dried and prepared, a hydrolysis polymerization product of iron is crystallized and separated out, and is mutually attracted to form the shape like an ore. The polysilicate iron/cationic starch composite flocculant is added with starch to react with the polysilicate iron in the preparation process, so that the composite flocculant has a new shape, the surface is quite rough, the middle of the composite flocculant is provided with a needle shape or a sheet shape which is inserted in the middle, a plurality of fine particles are attached to the needle and the sheet, and the whole composite flocculant is in an irregular coral shape. Due to the addition of the starch, the appearance of the composite flocculant is obviously changed, the specific surface area is increased, the surface is rougher, and a three-dimensional interweaving and superposing structural characteristic is presented. The structure enables the water sample to have larger contact area, and the water sample can be better contacted and adsorbed, so that the particulate matters in the water sample can be captured. After the starch is added, the molecular weight of the composite flocculant is increased, and impurities in water can be better removed through the adsorption bridging and net catching rolling sweeping effects. Meanwhile, due to quaternary amine ions carried on the cationic starch, ion impurities which are difficult to treat by the polysilicate iron flocculant can be treated through adsorption, and the treatment capacity of the composite flocculant is enhanced.
SEM-EDS analysis
And analyzing the surface appearance of the sample by using a scanning electron microscope, and scanning the surface element composition of the sample by combining an energy spectrometer. Sample treatment was identical to SEM analysis.
Fig. 7 is EDS analysis of the polysilicate-iron/cationic starch composite flocculant, and it can be seen that the main elements in the composite flocculant are O, Si, Fe, S, N, and a small amount of P and Ti, and the specific contents of each element are shown in table 1. The nitrogen element is from quaternary amine group of cationic starch, and the phosphorus element is from impurity of ilmenite in titanium dioxide production process.
TABLE 1 table of contents of elements of polysilicate-iron/cationic starch composite flocculant
| Element(s) | Wt％ | At％ |
| OK | 40.62 | 61.95 |
| SiK | 04.79 | 04.16 |
| PK | 02.76 | 02.18 |
| SK | 16.99 | 12.93 |
| TiK | 01.57 | 00.80 |
| FeK | 30.61 | 13.37 |
X-ray photoelectron spectroscopy (XPS) analysis
Elemental analysis was performed on the samples using an ESCALAB250Xi electron spectrometer under the following test conditions: monochromatic Alka (hv. 1486.6eV) radiation was used, with a power of 150W, 500 μm vertical spot, and the binding energy was calibrated with C1s284.8.
Fig. 8-11 are XPS analysis spectra of composite flocculants used for further analysis of the chemical composition of the composite flocculants. FIG. 8 is an XPS general spectrum, which shows that the composite flocculant contains Fe, O, Si and C elements and other elements, and impurities from waste acid have little influence on products and are not considered. FIG. 9 is an XPS plot of Fe2p with Fe (III) 2p at binding energy 711.1eV3/2The peak has 724.9eV binding energy of Fe (III) 2p1/2Peak, binding energy 713.3eV is the peak for Fe (II), pure Fe2O3Medium Fe (III) 2p1/2Peak binding energy of 724eV, Fe (III) 2p3/2The peak binding energy is 711eV, and the binding energy of the composite flocculant is higher than that of Fe2O3And the chemical reaction of the iron in the composite flocculant is shown to form Fe-O-Si bonds. The XPS plot of Si2p in FIG. 10 shows that the peak with a binding energy of 102.8eV fits well, indicating that Si exists only in this chemical environment. Pure SiO2The binding energy of the medium Si2p is 104.4eV, which is higher than that of the composite flocculant, and indicates that Si in the composite flocculant forms a new bond and forms a Fe-O-Si bond type. FIG. 11 is an XPS plot of O1s showing that the peaks can be divided into three peaks, 532.5, 531.7 and 531eV for the three O states. The peak at 532.5eV is the Fe-OH peak O1s, which is lower than pure Fe2O3O1s binding energy of medium 531.5 eV; 531.7eV is the peak for O1s in Fe-O-Si, whereas in Fe2O3O in (1) is 531.5eV, SiO2The middle O is 533.3eV, and the binding energy of the two is the same, which also proves the formation of Fe-O-Si bond; while the peak at 531eV corresponds to Fe-O. No chemical bond corresponding to the above was found at 536eV on both the polysilicate iron and the starch, and it is assumed that the chemical bond is an oxygen-containing chemical bond formed by dehydration condensation of the starch and the polysilicate iron.
Quantitative analysis of the scan results in FIG. 9 shows that Fe is present in the sample2+With Fe3+The ratio of the hydrogen peroxide to the flocculant is about 1:3.03, and this is caused by the fact that other reducing substances exist in the reaction system during the flocculant preparation process, so that the addition amount of the hydrogen peroxide is difficult to calculate, and the hydrogen peroxide solution is continuously added during the experimental operation process to prevent the hydrogen peroxide solution from changing color, but the hydrogen peroxide addition amount is insufficient due to the fact that the solution is dark in color and is difficult to judge accurately, and a small amount of ferrous ions are remained.
The same material characterization was performed on the polysilicate iron/cationic starch composite flocculant prepared in examples 2 to 4, and the obtained characterization results were highly consistent.
Second, adsorption experiment
The polysilicate iron/cationic starch composite flocculant prepared in the example 1-4 is used for treating aquaculture wastewater in a pond, 5 indexes of turbidity, chroma, COD, Total Nitrogen (TN) and Total Phosphorus (TP) are measured, and the measuring method comprises the following steps: adding 0.25mmol/L composite flocculant into 500mL water sample in a 1L beaker, quickly stirring for 2min by using magnetic stirring, slowly stirring for 10min at a quick stirring speed of 400r/min and a slow stirring speed of 80r/min, standing for a period of time, and taking supernatant liquid 4cm below the liquid surface for determination. And taking the culture wastewater added with the polysilicate iron flocculant as a reference. The results of the adsorption experiments are shown in table 2.
Table 2 adsorption experiment results of polysilicate iron/cationic starch composite flocculant for treating aquaculture wastewater
As can be seen from Table 1, the turbidity removal rate of the culture wastewater treated by the polysilicate iron flocculant is 85.8%, the chroma removal rate is 87.5%, the COD removal rate is 40.3%, the total nitrogen removal rate is 19.0%, and the total phosphorus removal rate is 66.6%. The turbidity removal rate of the polysilicate iron/cationic starch composite flocculant for treating aquaculture wastewater is more than 93.6%; the chroma removal rate is more than 93.3 percent, the COD removal rate is more than 49.6 percent, the total nitrogen removal rate is more than 30.3 percent, and the total phosphorus removal rate is more than 85.3 percent.
Compared with the polysilicate iron flocculant, the turbidity removal rate of the polysilicate iron/cationic starch composite flocculant for treating the culture wastewater is improved by more than 7.9 percent; the chroma removal rate is improved by more than 5.8 percent, the COD removal rate is improved by more than 9.3 percent, the total nitrogen removal rate is improved by more than 11.3 percent, and the total phosphorus removal rate is improved by more than 18.8 percent. Moreover, the flocculation time of the polysilicate iron/cationic starch composite flocculant is 30min, which is half of the flocculation time of the polysilicate iron flocculant, the flocculating constituent is large, the sedimentation speed is high, and the supernatant fluid is clear. Therefore, the polysilicate iron/cationic starch composite flocculant has a good treatment effect on aquaculture wastewater.
Claims (6)
1. The polysilicate-iron/cationic starch composite flocculant is characterized by comprising the following raw materials: the titanium dioxide waste acid, cationic starch, a sodium silicate solution, lime milk, hydrogen peroxide and alkali, wherein the molar ratio of silicon in the sodium silicate solution to iron in the titanium dioxide waste acid is 1:3-5, and the mass ratio of the iron in the titanium dioxide waste acid to the cationic starch is 1: 0.5-2.
2. The polysilicate-ferric/cationic starch composite flocculant of claim 1, wherein the molar ratio of silicon in the sodium silicate solution to iron in the titanium white waste acid is 1:4, and the mass ratio of iron in the titanium white waste acid to cationic starch is 1: 1.5.
3. The polysilicate-ferric/cationic starch composite flocculant of claim 1 or 2, wherein the titanium dioxide waste acid has a total iron concentration of 1.0-2.0 mol/L and a density of 1.6-1.9 g/mL.
4. The polysilicate-iron/cationic starch composite flocculant according to claim 1 or 2, wherein the alkali is a sodium hydroxide solution, the lime milk is a slurry obtained by dissolving calcium oxide in water, and the sodium silicate solution is a solution obtained by dissolving sodium silicate in water.
5. A method for preparing the polysilicate-iron/cationic starch composite flocculant according to any one of claims 1 to 4, wherein the method comprises the following steps:
(1) waste acid neutralization: adding lime milk into the titanium white waste acid, continuously stirring, and neutralizing until the pH value is 0.5-1.5 to obtain a mixture;
(2) and (3) suction filtration: performing suction filtration on the mixture to obtain filtrate which is neutralized waste acid for later use;
(3) curing polymerization: adding a sodium silicate solution into the neutralized waste acid, uniformly stirring, then adding hydrogen peroxide to oxidize ferrous iron in the solution into ferric iron, then adding an alkali to adjust the pH value of the solution to 2.5-3.0, then adding cationic starch, uniformly stirring, continuously adding the alkali to adjust the pH value of the solution to 3.5-4.0, standing for 1-3h to carry out curing polymerization reaction, thus obtaining the polysilicate iron/cationic starch composite flocculant.
6. The preparation method of the polysilicate-iron/cationic starch composite flocculant according to claim 5, wherein in the step (3), the molar ratio of the added amount of hydrogen peroxide to the divalent iron in the solution is 1-1.5: 2.
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