MXPA98003225A - A method for the treatment of sulfide minerals containing bismuto or concentrates of such mine - Google Patents

Abstract

The present invention relates to a method for pretreating sulphide minerals or sulfide mineral concentrates having a high bismuth content, which has a disturbing influence on the subsequent processing of the minerals or concentrates, to allow the minerals or concentrates are subsequently processed for the recovery of their valuable metal content, or at least facilitate such processing. The invention is characterized in that the ore or concentrate is leached with sulfuric acid for a predetermined period of time, while heat is supplied at a pH below 2, and thereafter separated from the leachate solution a leaching residue in the form of a product that is more poor in bismuth and more enriched with respect to the content of valuable metals that the material enters.

Description

A METHOD FOR THE TREATMENT OF SULFIDE MINERALS CONTAINING BISMUTO OR CONCENTRATES OF SUCH MINERAL DESCRIPTION OF THE INVENTION The present invention relates to a method for pretreating sulphide minerals or sulphide mineral concentrates containing bismuth in obstructing concentrations for the subsequent processing of the minerals or concentrates, to allow the minerals or concentrates to be processed for the recovery of their content < ie valuable metals, or at least facilitate such processing. There are sulphide minerals or sulphide mineral concentrates which, because of their high bismuth content, can not be used for the recovery of their valuable metal contents, or must at least be processed with great care, for example diluted with poor materials in bismuth. The problems are more noticeable with materials that must be processed primarily to produce refined copper, either pyrometallurgically or hydrometallurgically, since in both cases an electrolytic treatment process is carried out in which bismuth has a highly disturbing effect, and contributes towards the formation of mud / silt, with the risk of serious inclusions of impurities. Additionally, refined copper is required to include a maximum of 1 ppm bismuth. Limitations on bismuth content are also found for lead and tin products, which are at 50-100 ppm in the case of lead and at 100-500 ppm in the case of tin. The possibilities of handling bismuth in a process to produce iro talurgical copper for example, are limited, since bismuth is a relatively noble element, which is found in an elemental form in nature. Bismuth can be primarily separated as gaseous sulfur during the early stages of the cabre process, that is, during the melting and conversion stages, provided good contact is obtained between the copper matte and the gas, and that the molten material have a high temperature. The extraction of bismuth is not favored by the high quality matte, and the degree to which the air supplied to the process is enriched with oxygen. Despite the aforementioned possibilities of reducing the bismuth content, bismuth purification steps are often carried out separately at a later stage of the process, for example in vacuum refining, or in the steps of the soda treatment process, although this frequently results in low bismuth yields. In most copper melting furnaces, the maximum allowable bismuth content in the copper anodes used in the electrolytic refining process is as low as 50 ppm, to allow the aforementioned problems concerning the formations of the Mud and the serious inclusions of impurities caused by this, which imply contamination by bismuth among other things, can be avoided in the best possible degree. This means that the entrance of bismuth to the copper process must be limited, and with this - also the entry of bismuth-containing material. It is still necessary to reject certain materials, because although the extraction of bismuth during the pyro-etalurgical treatment process is relatively constant, it is too low. As will be easily understood, attention should be directed primarily to the productivity and economy of the process, which implies both high-quality killing and oxygen enrichment, which as mentioned above are not the best conditions under which it is eliminated. bismuth during the copper process.

The previous treatment of the copper concentrates has been proposed with the intention of reducing different contents of annoying impurities of the concentrate before its subsequent processing. Partial calcining can be used to reduce the arsenic content, but the bismuth content is only marginally influenced. The arsenic content, the content of antimony and the content of mercury can be reduced by leaching with sodium sulphide, although the bismuth content is not influenced to any degree by this treatment. In CA-A-1057310, Outokumpu has proposed a pretreatment in a rotary kiln at 750 ° C, in an atmosphere of sulfur vapor. This process eliminates 100% of arsenic, 50-60% of antimony, but only 20-30% of bismuth content. In EP-B-0138794, Boliden has proposed a method for primarily removing Sb from copper melt material. The method involves a separate chlorination step, with an essentially stoichiometric amount of chlorinating agent, in a spinning mill at temperatures of 450-750 ° C, where the Bi is also removed to a substantial degree. Bio-oxidative pretreatment, bio-leaching, to selectively leach bismuth from copper concentrates has also been proposed. The selectivity and usefulness of the bio-leachate for this purpose, however, would appear to be completely dependent on the mineralogical composition of the concentrate, and hence its use is limited to the treatment of certain specific concentrates of favorable composition.

The object of the present invention is to provide a method by which bismuth can be removed from sulfide ores or sulphide concentrates to a degree and with a selectivity with respect to the content of valuable metals so as to allow the material to be used generally for the pre-treatment of such materials, in such a way that the materials can be easily processed and their valuable metal content recovered. This object is achieved with a method having the characteristic features set forth in the following claims. Thus, the ore or concentrate concerned is leached with sulfuric acid for a given period of time, at a pH below 2, while heat is supplied. At the end of this predetermined time period, the leaching residue is extracted from the leachate solution in the form of a product that is purer relative to bismuth than the input material, and in which the valuable metal content has been enriched. The leaching process is preferably carried out. performed in a pE interval of 0-1. To achieve the best possible result, the leachate temperature will preferably exceed 50 ° C. The leaching process is preferably carried out in a series of mutually sequential leaching stages. The leach solution consumed can conveniently be treated with quicklime or limestone while adding air, to precipitate the amounts extracted by leaching bismuth, and possibly iron in the form of hydroxide, along with the sulfate content as gypsum. It is known that concentrated sulfuric acid or dilute sulfuric acid and air are capable of reacting with elemental bismuth to form Bi3 + ions, where the sulfuric acid is reduced to SO2. However, there are no previous descriptions in the literature for the effect that sulfuric acid would react in the same way with sulfidic bismuth compounds. Neither this is probable due to the very strong affinity of bismuth for sulfur. Despite this, leaching with sulfuric acid under certain specified conditions results, however, in the appreciable removal of bismuth, and additionally in the selective removal with respect to the valuable metal content, and should be considered remarkable and surprising. According to one theory, this may be due to the complicated substitution reactions in minerals between bismuth and valuable materials such as copper and silver. In addition to existing as elemental bismuth, bismuth is also present, for example in sulphidic copper minerals in the form of sulfide minerals such as: Matildite AgBiS2 bismuth sulfide Bi2S3 benjaminite P (Au, Cu) Bi2S9 hammarite PbzCu2Bi S9 galenabismutite PbBi2S4 CuBiS2 aikinita PbCuBiS3 The invention provides bismuth yields of. up to 90% and even higher, while the leaching of a valuable metal such as copper is not greater than at most 2%. Iron, on the other hand, is extracted by leaching to a greater degree, resulting in a yield of up to 5-6%. Thus, the pretreatment process of the invention results in a product, which in comparison with the inlet concentrate is purer with respect to Bi (and even Sb and As to some degree), and is also in applicable cases enriched with respect to valuable metals, since any iron present is eliminated, although it is well to a limited extent. The metal thus pretreated will be particularly attractive from various aspects with respect to processing its valuable metal content. The invention will now be described in greater detail, partly with reference to a diagram illustrating a preferred embodiment of the invention, including purification in solution and also with reference to an example illustrating leachate tests carried out on a laboratory scale. The attached drawing is a diagram illustrating the bismuth leaching according to the invention. A copper concentrate is taken from a sedimentation tank or filter with the relevant water balance and, optionally after being diluted with additional water, it is passed to a first leach tank with a solids content of 50-70%. Sulfuric acid is added to the tank, to keep the pH around 1. The contents of the tank are heated with heat taken from an external source. A suitable temperature is 90 ° C. The contents of the tank are continuously transferred to a second tank connected in series, and from there to a third and a fourth tank. The volume of the tanks and the residence time in the respective tanks are selected with respect to a predetermined total leach time. This time of leachate is selected, in turn, on the basis of the desired yields from the composition of the concentrate concerned. If appropriate and if desired, S02 can be added to the last tank to precipitate leached copper. After a separation / washing step of the solid / liquid, a bismuth-free copper concentrate is extracted and enriched for further processing in a melting furnace. As shown in the diagram, the leachate solution and the aggregate wash water are divided into two parts, where the Bi3 +, Fe2 + / Fe3 + present in a part are precipitated with limestone, while air is supplied at a pH in the 3-5 region. The precipitate with bismuth hydroxide, iron hydroxide and gypsum is separated downstream of the separation stage + solid / liquid washing. The residual solution, which can still contain copper in the form of Cu2 + ions, can be returned to the leaching stage as an addition of liquid. Copper can precipitate from an extraction taken from this return flow, if desired. The rest of the leachate solution is returned to the first leachate tank as a process liquid.

Example It was leached in a series of copper concentrates from Aitik, which consists mainly of chalcopyrite and pyrite minerals. The bismuth content was 120 grams / t, and existed in the form of several different minerals, ie those mentioned above matildite, bismuth sulfide, benjaminite, hammarite, galenobismutite, emollite and aikinite. A smaller part of the total Bi was present as elemental bismuth. The tests were carried out at a milled product density of about 45% solids. The leachate process was studied under different conditions for twenty hours. 500 grams of concentrate and € 10 milliliters of raw water from Aitik were mixed in each test. The pH was continuously checked during the tests, and adjusted with H2SO4 or UaOH. Samples of leaching solution will be taken at five time points: 0.5, 1.0, 2.0, 5.0 and 24 hours. The test conditions and results have been placed in the Table below: TABLE Test pH Temperature Performance of Bi Performance No. in percentage Cu in percentage 2 hr 5 hr 24 hr 2 hr 5 hr 24 hr 1 0 25 36 35 35 0.3 0.4 0.7 2 1.0 25 28 26 34 0.2 0.3 0.4 3 0 90 70 80 83 0.6 0.9 1.7 4 1.0 90 72 80 92 0.3 0.4 0.6 0.5 55 40 54 75 0.4 0.6 1.3 6 0.5 5.5 40 54 75 0.4 0.6 1.3 7 1.5 90 35 48 42 0.2 0.3 0.3 8 2.0 90 4 2 0 0.2 0.3 0.3 9 2.5 90 0 2 0 0.1 0.1 0 3.0 90 0 0 0 0 0 0 Optimal conditions for bismuth leaching existed at a pH of 0-1 and a temperature of 90 ° C, where yields were as high as about 70% already after two hours, while copper yields were at same time very low, around 0.%. The yields of Bi were never higher than about 30% at room temperature. At a temperature of 55 ° C the yields increase greatly. Practically no leachate was obtained from either Bi or Cu at a pH = 2 or higher. Suitable leach times for the type of concentrate concerned are established by appropriate similar laboratory tests, although restricted to the most optimal conditions at the selected leach temperatures. The necessary leaching time is governed by the higher residual bismuth content desired in the concentrate. It may still be relevant and economically beneficial to decrease the bismuth content to a very low concentration when possible with respect to possible losses of valuable metal in the treatment process. In other words, the leaching time can be determined primarily with respect to the market situation, ie the value of the concentrate of different degrees of purity with respect to the bismuth. The method of the invention can thus be easily and safely adapted to current and market technical requirements, even with respect to minerals and concentrates of the most varied compositions.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following:

Claims (4)

1. A method to pre-treat sulphide minerals or sulfide ore concentrates that have a high bismuth content, which has a disturbing influence on the subsequent processing of minerals or concentrates, to allow minerals or concentrates to be further processed for recovery of its valuable metal content, or at least facilitate such a process, the method is characterized in that the ore or concentrate is leached with sulfuric acid for a predetermined period of time, while heat is supplied at a pH below 2, and after that the ore or concentrate is separated from the leachate solution in a concentrated form, which is poorer in bismuth and enriched with respect to the content of valuable metals.

2. A method according to claim 1, characterized in that it is leached in the pH range of 0-1.

3. A method according to claims 1 and 2, characterized in that heat is supplied during the leaching process, to maintain a temperature above about 50 ° C, preferably around 90 ° C.

4. A method according to claims 1-3, characterized in that it is leached in two or more consecutive sequential leaching stages. . A method according to claims 1-4, characterized in that the leachate solution is treated subsequent to the extraction of the leach residue with quicklime or limestone, while air is supplied, to precipitate the leached quantities of bismuth and iron in the form of hydroxide, together with plaster.