Leach liquor purification

Purification of leach liquors - as an example, mention may be made of the removal of cadmium and thallium from a zinc sulfate solution. In this case it is very convenient to use metallic zinc as a cementing metal, since the zinc that enters into solution is recovered subsequently. 

A recent and extremely important development lies in the application of the technique of liquid extraction to metallurgical processes. The successful development of methods for the purification of uranium fuel and for the recovery of spent fuel elements in the nuclear power industry by extraction methods, mainly based on packed, including pulsed, columns as discussed in Section 13.5 has led to their application to other metallurgical processes. Of these, the recovery of copper from acid leach liquors and subsequent electro-winning from these liquors is the most extensive, although further applications to nickel and other metals are being developed. In many of these processes, some form of chemical complex is formed between the solute and the solvent so that the kinetics of the process become important. The extraction operation may be either a physical operation, as discussed previously, or a chemical operation. Chemical operations have been classified by Hanson(1) as follows ... 

Concentration/purification by solvent extraction usually involves four steps (a) extraction of uranium from the leach liquor in a solvent, (b) scrubbing to remove impurities from the solvent, (c) stripping to remove uranium from the solvent, and (d) regeneration of the solvent. The solvent phase in solvent extraction will contain the extractant that complexes uranium to make it soluble in the organic phase, a diluent, an inexpensive material to dilute the extractant, and a modifier to improve the solubility of the extractant in the diluent. Typical extractants are amines with isode-canol acting as a modifier to improve the amine solubility in a diluent such as kerosene. The typical chemistry of the extraction would involve the reactions... 

The improved capabilities of LIX 64 N reagent for recovery, purification, and concentration of copper values from acidic leach liquors were described by DeMent and Merigold (DlO). The leaching of copper sulfide flotation concentrates with subsequent recovery of copper by LIX 64 N was shown to be technically feasible. This extractant loads and strips faster, is more effective in extracting copper from a lower pH solution, has considerably less secondary entrainment, has better iron rejection, and may be used at levels up to 30 vol. % in kerosene without aqueous entrainment. Use of the reagent in operating pilot and commercial plants is also discussed. 

In the various solvent-extraction circuits employed in this process, use is made of a solution of D2EHPA in kerosene as the extractant. The selective recovery of the various metals is achieved by careful control of the equiUbrium pH value of the aqueous phases in the multistage extraction and stripping operations. After the leach liquor has passed through two separate circuits, each of which comprises five stages of extraction and four of stripping, the europium product is obtained initially as a solution of europium(III) chloride. Further purification of the product is accomplished by reduction with amalgamated zinc to Eu +, which is by far the most stable of the divalent lanthanide ions with respect to the reduction of water cf. the redox potentials of the Eu /Eu and Sm /Sm + couples, which are —0.43 and —1.55 V respectively ). Sulfuric acid is added to the... 

In 2003, the world zinc production was 9 880000 tons [55]. The most important zinc production process is the electrolytic or roast-leach-electrowinning (RLE) process. This was first used in 1916 by Anaconda and Cominco. The industrial processes of zinc production use zinc oxides as raw materials. The most important natural raw material is zinc sulfide, and, therefore, it needs to be roasted and converted to oxide. The main problem in leaching and liquor purification is separation of zinc and iron. As dissolution of iron cannot be avoided, it must be precipitated from the zinc sulfate solution. Impurities still present after the iron precipitation stage can lead to lower current efficiency and impurities in the zinc cathode. Therefore, the solution is further purified by cementation with zinc powder. 

Copper may also be recovered from leach solutions electrolytically. Electrowinning requires the use of an insoluble anode such as hard lead, comparable to the liberator cell used for liquor purification in copper electrorefining. Consequently, there are net electrochemical reactions involved in electrowinning (Eqs. 13.20 and 13.22), as opposed to the situation with electrorefining, so that about 1.7 V are required for this step. This results in a much higher electrical power consumption of about 2.8 kWh/kg copper for electrowinning, compared to about 0.2 kWh/kg for electrorefining. 

I rt 1 of Table 5.19 lists mills using carbonate leaching. There is no standard process for recovery of uranium from carbonate leach liquors. The trend is away from precipitation with NaOH as crude NajUj07 toward further purification as by UO4 precipitation at Rio Algom or by ion exchange followed by precipitation as (NH4)3U207 at George West. 

The principal steps in producing refined thorium compounds from thorium-bearing ores are concentration of thorium minerals, extraction of thorium from concentrates, purification or refining of thorium, and conversion to metal or the thorium compound finally wanted. This section describes the concentration of monazite, the principal source of thorium in the past the extraction of thorium from monazite and the recovery of thorium from leach liquors by solvent extraction. Purification of thorium is described in Sec. 9 and conversion in Sec. 10. 

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