Dilute acid leaching

It is convenient to discuss dilute acid leaching first. Much of the equipment and some of the chemical principles are common with dilute alkali leaching. Other breakdown techniques are only employed when these cheaper processes have been foimd unsuccessful. 

Some secondary materials, which have been produced geologically as a result of natural chemical action on the primary minerals, have their uranium already in the hexavalent state and are fairly readily leached by dilute sulphuric or hydrochloric acid without an oxidant these include carnotite, autunite, and torbernite. Other secondary minerals such as davidite and pyrochlore are more refractory and are not amenable to dilute acid leaching. 

Unlike dilute acid leaching vessels, those handling hot concentrated sulphuric acid may have to be fitted with lids and adequately vented to remove corrosive acid fumes. More stringent safety measures than with... 

A similar non-aqueous process has been decribed using iso-octyl phosphoric acid, monododecyl phosphoric acid or monoheptadecyl phosphoric acid as solvents, none of which require the ammonium nitrate addition. Methyl ethyl ketone, other ketones, or kerosene are suitable diluents. The sulphuric acid usage is much less than that normally required for, for example, a dilute acid leach of the camotite ore used, since the high proportion of lime present in the ore is not taken into solution. Hydrochloric acid is preferable for backwashing the uranium. 

Dilute acid leaching was taken to teat the magnetic concentrate to remove lead. Under certain conditions, lead content of leached concentrate decreased to 0.19%, which can basically met the requirements for iron ore concentrate in the steel industry. The mechanism of lead separation from the leached ore was die dissolution of lead sulfate and lead oxide after reacting wifli hydrochloric acid during the leaching process. 

Production and Economic Aspects. Thallium is obtained commercially as a by-product in the roasting of zinc, copper, and lead ores. The thallium is collected in the flue dust in the form of oxide or sulfate with other by-product metals, eg, cadmium, indium, germanium, selenium, and tellurium. The thallium content of the flue dust is low and further enrichment steps are required. If the thallium compounds present are soluble, ie, as oxides or sulfates, direct leaching with water or dilute acid separates them from the other insoluble metals. Otherwise, the thallium compound is solubilized with oxidizing roasts, by sulfatization, or by treatment with alkaU. The thallium precipitates from these solutions as thaUium(I) chloride [7791 -12-0]. Electrolysis of the thaUium(I) sulfate [7446-18-6] solution affords thallium metal in high purity (5,6). The sulfate solution must be acidified with sulfuric acid to avoid cathodic separation of zinc and anodic deposition of thaUium(III) oxide [1314-32-5]. The metal deposited on the cathode is removed, kneaded into lumps, and dried. It is then compressed into blocks, melted under hydrogen, and cast into sticks. 

Vanadium powder can be prepared by substituting V2O2 for the V20 as the vanadium source. The heat generated during the reduction of the trioxide is considerably less than for the pentoxide, so that only soHd products are obtained. The powder is recovered from the product by leaching the slag with dilute acid. 

Recovery of Bismuth from Tin Concentrates. Bismuth is leached from roasted tin concentrates and other bismuth-beating materials by means of hydrochloric acid. The acid leach Hquor is clarified by settling or filtration, and the bismuth is precipitated as bismuth oxychloride [7787-59-9] BiOCl, when the Hquors are diluted usiag large volumes of water. The impure bismuth oxychloride is usually redissolved ia hydrochloric acid and reprecipitated by diluting several times. It is then dried, mixed with soda ash and carbon, and reduced to metal. The wet bismuth oxychloride may also be reduced to metal by means of iron or 2iac ia the presence of hydrochloric acid. The metallic bismuth produced by the oxychloride method requites additional refining. 

Figure 5. Histogram Th/U for clinopyroxenes in peridotites and pyroxenites from the Ronda peridotite massif Concentrations were measured by isotope dilution mass spectrometry in acid-leached clinopyroxenes. This histogram shows that pyroxenites do not have larger Th/U ratios than peridotites. Thus, the correlation found between ( °Th/ U) and Th/U cannot be explained by mixing of peridotite and pyroxenite melts as advocated in Sigmarsson et al. (1998). Data from Hauri et al. (1994) and Bourdon and Zindler (unpublished). It can be shown with a simple Student t-test that the two populations are indistinguishable.

Beryl Melted and quenched An amorphous glassy product is produced. Dilute sulfuric acid leaching... 

Large-scale winning of copper by acidic leaching of copper ores sometimes results in waste solutions containing appreciable amounts of uranium. The uranium bearing aqueous raffinate from copper extraction is usually a dilute sulfuric acid solution. Uranium can be recovered using the same technique as described in section 12.3.1. A typical example is uranium production at the Olympic Dam mine in Australia, where the copper ore bodies are estimated to contain a total of over a million metric tons of uranium. 

Vanadium usually is recovered from its ores by one of two processes, (1) leaching raw mineral with hot dilute sulfuric acid, and (2) roasting ore with common salt to convert vanadium into water soluble sodium vanadates. In the sulfuric acid leaching process, vanadium is extracted from acid leach liquors by solvent extraction with an aliphatic amine or an alkyl phosphoric acid in kerosene. The organic solvent extract then is treated with an aqueous solution of ammonia in the presence of ammonium chloride to convert vanadium into ammonium metavanadate. Alternatively, the organic extract is treated with dilute sulfuric acid or an aqueous solution of soda ash under controlled conditions of pH. Vanadium is precipitated from this solution as a red cake of sodium polyvanadate. 

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