Hydrochloric acid leaching

Hydrochloric acid digestion takes place at elevated temperatures and produces a solution of the mixed chlorides of cesium, aluminum, and other alkah metals separated from the sUiceous residue by filtration. The impure cesium chloride can be purified as cesium chloride double salts such as cesium antimony chloride [14590-08-0] 4CsCl SbCl, cesium iodine chloride [15605 2-2], CS2CI2I, or cesium hexachlorocerate [19153 4-7] Cs2[CeClg] (26). Such salts are recrystaUized and the purified double salts decomposed to cesium chloride by hydrolysis, or precipitated with hydrogen sulfide. Alternatively, solvent extraction of cesium chloride direct from the hydrochloric acid leach Hquor can be used. 

Hibemia-Chemie has described a vapor-phase process that passes fresh and recycled 85 wt % phosphoric acid over a catalyst of hydrochloric acid-leached bentonite impregnated with phosphoric acid. Catalyst activity was claimed to remain constant over a period of one year at the following conditions (126) ... 

Similar result was obtained for skeletal Si . The solubility of Si in the a -A1 solid solution is negligibly small so that the two phases a -A1 and relatively coarse Si existed in the conventionally prepared Al-Si alloy. By hydrochloric acid leaching, only the coarse stable Si remains after leaching, so that it is difficult to form fine Si particles by leaching. In this case, the rapid solidification increases the solubility to about 12 at%. The specific surface area of skeletal Si formed from RWA was in the range of 65-75mVg and the mean particles size was about 30-50nm by direct observation of the skeletal Si. 

Under certain conditions, there are definite advantages in using hydrochloric, nitric, or other acids to carry out a dissolution step. In their evaluation of proposed processes for the recovery of alumina, Peters ei al. (P8) cited earlier experimental work which showed that both hydrochloric and sulfuric acid are equally good in extracting alumina from calcined clay (TIO). In the separation of the leach liquor from the silica residue by filtration, the chloride solution rapidly separated, while the sulfate solution did not separate easily. In addition to ease of filtration, the hydrochloric acid leach also made the later removal of iron easier. The insolubility of titanium dioxide in hydrochloric acid also eliminated another separation problem. Under this particular situation, hydrochloric acid was the natural choice. As in most large leaching operations, the acid would be recovered and recycled. 

Sutherland R. A. (2002) Comparison between non-residual A1 Co, Cu, Fe, Mn, Ni, Pb and Zn released by a three-step sequential extraction procedure and a dilute hydrochloric acid leach for soil and road deposited sediment. Appl. Geochem. 17, 353 —365. 

During leaching, not only the rare-earths but also impurity elements such as calcium, sodium, phosphorus, chlorine, magnesium, antimony, manganese, iron, and aluminum were dissolved. In order to remove these impurities, hydroxide precipitation at pH 10 with ammonia and the subsequent hydrochloric acid leaching of the precipitate were studied. By the hydroxide precipitation, sodium, phosphoms, chlorine, calcium, and magnesium remained in the supernatant and rare earths formed a precipitate. After dissolving the precipitate with hydrochloric acid, rare earths were recovered by the oxalate... 

Reduction and hydrochloric acid leach process Cuprion ammoniacal leach process Reduction and hydrochloric acid leach process High-temperature and high-pressure sulfuric add leach process ... 

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