GB826242A - Process for wet-treating arseniuretted or sulfarsenidic materials, particularly ores, containing cobalt and/or nickel, together with iron in variable proportion - Google Patents

Abstract

Ores containing arsenic, iron and cobalt and/or nickel, and possibly sulphur, are first leached with nitric acid and sulphuric acid, the solution (which contains cobalt and/or nickel sulphates) is separated from the solid (consisting of arsenious oxide, unreacted ore and insolubles) and the latter is further leached with nitric acid alone, preferably after removing arsenious oxide by hot aqueous leaching. In the first step, the sulphuric and nitric acids are sufficient (a) to convert 80 to 85% of the metals present in the starting material which form water-soluble sulphates, to water-soluble sulphates, and additionally to provide sufficient sulphuric acid to prevent metal salt precipitation on cooling, and (b) to convert 80 to 85% by weight of the arsenic in the starting material to a mixture of As2O3 and As2O3 in which the amount of As2O5 is less than stoichiometrically equivalent to the dissolved iron but is large enough to secure in the reaction mixture, if cooled, together with As2O3 remaining dissolved, a total amount of dissolved arsenic corresponding to about one stoichiometric equivalent of arsenic per equivalent of dissolved iron. In the second step, the nitric acid is preferably used in the amount required to convert the remainder of the metals to soluble nitrates thereof and the remainder of arsenic to a mixture of As2O3 and As2O5 in which As2O3 is present to the extent of at least 85% by weight. In the preferred embodiment, the ore is crushed and ground and sufficient sulphuric acid is added to provide 30-40 gms./litre of free H2SO4 in the liquid after the reaction in addition to that required to form soluble sulphates. The above-defined quantity of nitric aic is then added. During the reaction the temperature may rise to 100 DEG C., and nitrous vapours are produced which may be reoxidized and used again. The mixture may be filtered hot or, preferably, cooled to precipitate the As2O3 and filtered. The residue is suspended in the mother liquor from a previous As2O3 crystallization and the mixture boiled and hot filtered. As2O3 is recovered by cooling the liquid (to which one or more of sulphuric or hydrochloric acids or an anionic wetting agent such as a mixture of fatty secondary alcohol sulphonates may be added). The residue from hot filtration is then leached with nitric acid alone, cooled to crystallize As2O3 and filtered. The evolved nitrous vapours may be re-oxidized to nitric acid and reused. The liquor and washings are returned to the first leaching stage, where the cobalt and nickel nitrates contained therein are converted to sulphates. The residue is treated for recovery of As2O3 as before. The above-mentioned wetting agent is added to the solution obtained from the first leaching operation, and the Fe/As ratio adjusted, if desired, to 0.8-1.2 by adding solid As2O3 or the As2O3 mother liquor or ferric hydroxide, and chlorine or a hypochlorite used to oxidize the iron and arsenic. A slurry of calcium carbonate is then added to give a pH of 4-4.5; an anionic wetting agent such as that referred to above may be present in the slurry or added therewith. The precipitate of ferric arsenate thus formed is removed and the solution treated to recover cobalt oxide and nickel carbonate, the latter by acidifying with sulphuric acid and neutralizing with a cold saturated solution of sodium carbonate.