Cobalt from arsenical concentrates

The extraction of cobalt from arsenical concentrates consisting of autooxidation acid leaching under pressure, separation, purification, hydrogen reduction of ammoniacal leach solution, and removal of sulfur and granulation of the metal was described by Mitchell (M37). The final product contained 95.6% cobalt, 3.90% nickel, and 0.03% arsenic compared to the feed concentrate with an assay of 17.5% cobalt, 1% nickel, and 24% arsenic. 

Final solutions from both pressure and atmospheric leach tests were submitted for chemical analysis, and the results are presented in Table VIA. The concentrations of cobalt, nickel and selenium in the final solutions were not significantly different. Arsenic, antimony and tellurium levels were about the same or lower in the solution generated in pressure leaching (the arsenic concentration was substantially lower in the pressure leach liquor for... 

Analysis of zinc solutions at the purification stage before electrolysis is critical and several metals present in low concentrations are monitored carefully. Methods vary from plant to plant but are highly specific and usually capable of detecting 0.1 ppm or less. Colorimetric process-control methods are used for cobalt, antimony, and germanium, turbidimetric methods for cadmium and copper. Alternatively, cadmium, cobalt, and copper are determined polarographicaHy, arsenic and antimony by a modified Gutzeit test, and nickel with a dimethylglyoxime spot test. 

Many heavy metals react with dithiol to give coloured precipitates, e.g. bismuth, iron(III), copper, nickel, cobalt, silver, mercury, lead, cadmium, arsenic, etc. molybdate and tungstate also react. Of the various interfering elements, only arsenic distils over with the tin when a mixture is distilled from a medium of concentrated sulphuric acid and concentrated hydrobromic acid in a current of carbon dioxide. If arsenic is present in quantities larger than that of the tin it should be removed. 

Concentrated hydrochloric acid also dissolves the trichloride, about 100 g. of the latter dissolving in 1 litre of acid at 100° C.7 Dissolution in hydriodic acid is accompanied by evolution of heat and the triiodide is formed.8 Ethyl iodide reacts similarly.9 Double decomposition reactions occur w hen arsenic trichloride is heated with phosphorus triiodide, stannic iodide or germanium iodide, the reactions being complete.10 Similarly, potassium iodide heated with arsenic trichloride in a sealed tube at 210° C., and potassium bromide at 180° to 200° C., form respectively arsenic triiodide and tribromide.11 Stannous chloride, added to the solution in hydrochloric acid, causes reduction to arsenic (see p. 29). Arsenic trichloride may be completely separated from germanium chloride by extraction with concentrated hydrochloric acid.12 Ammonium, sodium and cobaltic chlorides react with arsenic trichloride to form additive compounds with magnesium, zinc and chromic chlorides there is no reaction.13... 

In the trace-element data, the first principal component accounts for over 50% of the variance. Aluminum and most other elements correlate positively with the first principal component, a pattern consistent with simple dilution (22,23) - in this case, by quartz sand temper. In contrast, the second principal component (accounting for an additional 15% of the variance) represents the heavy mineral sand component (Ti, Hf, Zr), which negatively covaries with cobalt, manganese, antimony, and arsenic. The Qo and Qm clays from the lowlands are broadly similar in composition (Figure 5). The Qc deposit differs significantly, i.e., the low PC2 scores indicate high concentrations of the characteristic of heavy mineral sands (Ti, Hf, Zr). The Qk and Tp samples span range of composition, but are represented by only 2 samples each. 

At Modum Blafargeverk cobalt was produced from an ore with arsenic content. The factory was abandoned at the end of the last century. Soil and plant analysis showed a greater arsenic content than normal (Lag, 1978). Most probably the concentrations in the plants were much higher as long as the factory was driven. Comparison with preliminary figures given by FAO and WHO (1974) for acceptable limits for man show that it should not be dangerous now to use the plant products for nutrition. 

Other compounds may be found in leachate from landfills, e.g., borate, sulfide, arsenate, selenate, barium, lithium, mercury, and cobalt. In general, however, these components are not often measured when they are measured, they are usually present in very low concentrations and are considered only of secondary importance. 

The average trace-element concentrations of seven xtl MMs from the Cap Prudhomme collection are listed in Table 18.14 based on data published by Kurat et al. (1994). The enrichment or depletion of trace elements in the MMs relative to average rocks of the continental crust (Taylor and McLennan 1985) was expressed as the logarithm to the base 10 of the MM crustal-rock ratios. The resulting distribution of data points in Fig. 18.31 indicates that the MMs are strongly enriched in iridium and gold as well as in nickel, chromium, selenium, iron, cobalt, arsenic, and antimony relative to crustal rocks. 

Sulfur and several sulfides, highly insoluble precipitates with solubility products as low as 1.6 X 10 for mercuric sulfide, have been used to concentrate trace metals from water. Sulfur, produced from (NH4)aS and HNO3 ( 0), coprecipitated several metals including mercury. Iron(III) sulfide (also used in a commercial process SULFEX) removes several metals (61) and is better than hydroxide in the presence of EDTA and other chelating agents (62). Lead sulfide has been used to collect silver for aqueous solution (63), molybdenum sulfide to collect arsenic from 2 M hydrochloric acid solution (64), and copper sulfide to concentrate cobalt and zinc from seawater (65). 

The properties of anion-exchange resins of several types have been described in detail by Kraus and Nelson 351-356) and others (557, 358). Selenium(IV), tellurium(IV), and arsenic(III) and (V) can be extracted from a variety of media 359-361). Thallium(III) and antimony(V) can be separated using the iodide and chloride forms of Dowex-1 (5(52, 363). Beryllium(II) was efficiently extracted by the carbonate form 364, 365) and chromium(III) and lead(II) by the phosphate form of AV-17 resin 366). Zinc(II) can be removed from a solution containing several metals (5(57, 368) and silver in concentrations at the 0.04-ppb level can be extracted from seawater (5(59). Cobalt(II), zinc(II), antimony(III), silver(I), and iron(III) ions have also been extracted from spiked seawater samples by anion exchange even though the actual form of the ions in the aged solution was uncertain (570). Anion resins have been modified with Trilon B (577) and with a-hydroxyisobutyronitrile (572) to increase the extraction of several trace-metal pollutants. Amberlite IRA 400 treated with the sulfonic acid derivative of dithizone can be used to concentrate heavy metals (575). 

Arsenic-containing concentrates (from cobaltite ores) are roasted in a fluidized bed at 700°C to remove most of the arsenic as As Oj. After leaching with hydrochloric or sulfuric acid the purified leach solution can be used for electro-extraction of cobalt or for precipitation of cobalt as carbonate. 

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