Anode slime is the insoluble product deposited at the bottom of the electrorefining tank during electrorefining of copper. It generally contains Cu, Ni, Se, Te, Ag, Au, platinum group metals (PGM), Pb, Ba, Fe, etc. Owing to the presence of valuable metals and metalloids in the anode slime, numerous approaches have been made by the researchers to extract them following pyro-, pyrohydro-, hydropyro-, hydrometallurgical, etc. routes. In the present paper the various processing routes with the special emphasis on plant practice and precious metals recovery from anode slime have been described systematically. Since the understanding of the process chemistry is considerably aided by the formation and characterisation studies of the slime, these aspects have also been included.

Processing of copper electrorefining anode slime: a review

Optimisation of the chlorination of gold in decopperized anode slime in aqueous medium

A hydrometallurgical process is provided for separating heavy metal nuisance elements such as As, Sb, Bi, Sn and Pb from precious metals and/or selenium. The process can be used as a step in an overall hydrometallurgical process for treating refinery residues such as anode slimes for the separation and recovery of valuable metal values.

Hydrometallurgical processing of precious metal-containing materials

The current study outlines the electrochemical recovery of tellurium from a metallurgical plant waste fraction, namely Dore slag. In the precious metals plant, tellurium is enriched to the TROF (Tilting, Rotating Oxy Fuel) furnace slag and is therefore considered to be a lost resource—although the slag itself still contains a recoverable amount of tellurium. To recover Te, the slag is first leached in aqua regia, to produce multimetal pregnant leach solution (PLS) with 421 ppm of Te and dominating dissolved elements Na, Ba, Bi, Cu, As, B, Fe and Pb (in the range of 1.4–6.4 g dm−3), as well as trace elements at the ppb to ppm scale. The exposure of slag to chloride-rich solution enables the formation of cuprous chloride complex and consequently, a decrease in the reduction potential of elemental copper. This allows improved selectivity in electrochemical recovery of Te. The results suggest that electrowinning (EW) is a preferred Te recovery method at concentrations above 300 ppm, whereas at lower concentrations EDRR is favoured. The purity of recovered tellurium is investigated with SEM–EDS (scanning electron microscope–energy dispersion spectroscopy). Based on the study, a new, combined two-stage electrochemical recovery process of tellurium from Dore slag PLS is proposed: EW followed by EDRR.

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Electrochemical recovery of tellurium from metallurgical industrial waste

Sami Virolainen Hydrometallurgical recovery of valuable metals from secondary raw materials Lappeenranta 2013 89 p Acta Universitatis Lappeenrantaensis 554 Diss Lappeenranta University of Technology ISBN 978-952-265-524-0, ISBN 978-952-265-525-7 (PDF) ISSN-L 1456-4491, ISSN 1456-4491 Wastes and side streams in the mining industry and different anthropogenic wastes often contain valuable metals in such concentrations their recovery may be economically viable These raw materials are collectively called secondary raw materials The recovery of metals from these materials is also environmentally favorable, since many of the metals, for example heavy metals, are hazardous to the environment This has been noticed in legislative bodies, and strict regulations for handling both mining and anthropogenic wastes have been developed, mainly in the last decade In the mining and metallurgy industry, important secondary raw materials include, for example, steelmaking dusts (recoverable metals eg Zn and Mo), zinc plant residues (Ag, Au, Ga, Ge, In) and waste slurry from Bayer process alumina production (Ga, REE, Ti, V) From anthropogenic wastes, waste electrical and electronic equipment (WEEE), among them LCD screens and fluorescent lamps, are clearly the most important from a metals recovery point of view Metals that are commonly recovered from WEEE include, for example, Ag, Au, Cu, Pd and Pt In LCD screens indium, and in fluorescent lamps, REEs, are possible target metals Hydrometallurgical processing routes are highly suitable for the treatment of complex and/or low grade raw materials, as secondary raw materials often are These solid or liquid raw materials often contain large amounts of base metals, for example Thus, in order to recover valuable metals, with small concentrations, highly selective separation methods, such as hydrometallurgical routes, are needed In addition, hydrometallurgical processes are also seen as more environmental friendly, and they have lower energy consumption, when compared to pyrometallurgical processes In this thesis, solvent extraction and ion exchange are the most important hydrometallurgical separation methods studied Solvent extraction is a mainstream unit operation in the metallurgical industry for all kinds of metals, but for ion exchange, practical applications are not as widespread However, ion exchange is known to be particularly suitable for dilute feed solutions and complex separation tasks, which makes it a viable option, especially for processing secondary raw materials Recovering valuable metals was studied with five different raw materials, which included liquid and solid side streams from metallurgical industries and WEEE Recovery of high purity (997%) In, from LCD screens, was achieved by leaching with H2SO4, extracting In and Sn to D2EHPA, and selectively stripping In to HCl In was also concentrated in the solvent extraction stage from 44 mg/L to 65 g/L Ge was recovered as a side product from two different base metal process liquors with Nmethylglucamine functional chelating ion exchange resin (IRA-743) Based on equilibrium and dynamic modeling, a mechanism for this moderately complex adsorption process was suggested Eu and Y were leached with high yields (91 and 83%) by 2 M H2SO4 from a fluorescent lamp precipitate of waste treatment plant The waste also contained significant amounts of other REEs such as Gd and Tb, but these were not leached with common mineral acids in ambient conditions Zn was selectively leached over Fe from steelmaking dusts with a controlled acidic leaching method, in which the pH did not go below, but was held close as possible to, 3 Mo was also present in the other studied dust, and was leached with pure water more effectively than with the acidic methods Good yield and selectivity in the solvent extraction of Zn was achieved by D2EHPA However, Fe needs to be eliminated in advance, either by the controlled leaching method or, for example, by precipitation 100% Pure Mo/Cr product was achieved with quaternary ammonium salt (Aliquat 336) directly from the water leachate, without pH adjustment (pH 137) A Mo/Cr mixture was also obtained from H2SO4 leachates with hydroxyoxime LIX 84-I and trioctylamine (TOA), but the purities were 70% at most However with Aliquat 336, again an over 99% pure mixture was obtained High selectivity for Mo over Cr was not achieved with any of the studied reagents Ag-NaCl solution was purified from divalent impurity metals by aminomethylphosphonium functional Lewatit TP-260 ion exchange resin A novel preconditioning method, named controlled partial neutralization, with conjugate bases of weak organic acids, was used to control the pH in the column to avoid capacity losses or precipitations Counter-current SMB was shown to be a better process configuration than either batch column operation or the cross-current operation conventionally used in the metallurgical industry The raw materials used in this thesis were also evaluated from an economic point of view, and the precipitate from a waste fluorescent lamp treatment process was clearly shown to be the most promising

Hydrometallurgical recovery of valuable metals from secondary raw materials

A hydrometallurgical process for recovering precious metals, such as gold, silver, selenium, and tellurium etc. from anode slime has been developed and tested successfully. The process comprises three major unit operations: leaching, liquid-liquid extraction, and reduction. The decopperized anode slime is first leached with nitric acid at an elevated temperature to obtain a leach solution containing at least about 95% by weight of the silver content, 96% by weight of the selenium content and 76% by weight of the tellurium content of the decopperized anode slime. Silver in the nitric acid leach solution is recovered in the form of silver chloride. Subsequent to the recovery of silver chloride, the selenium, tellurium, copper and other impurities-containing solution is denitrated and chlorinated by a liquid-liquid extraction technique. This selenium, tellurium, copper and other impurities-containing chloride solution is treated to separate tellurium from selenium, copper and other impurities by a liquid-liquid extraction technique. Selenium and tellurium are then recovered individually by passing sulfur dioxide through the selenium-containing and tellurium-containing solutions. The nitric acid leach residue is treated with aqua regia to leach gold and other impurities at an elevated temperature for a period of about 1 to 4 hours. The gold-containing solution is sent to separate gold from other impurities by a liquid-liquid extraction technique. Gold with a purity of greater than 99.9% is recovered by introducing a reducing agent to the gold-loaded organic extractant at an elevated temperature for a period of about 2 to 4 hours. This newly developed process is pollution-free, energy-saving, and economic to compare with conventional pyrometallurgical processes.

I-Sine Shaw

Papers

A hydrometallurgical process for recovering precious metals from anode slime