Abstract: A process for treating a pyrite concentrate containing silver, copper and zinc to recover the metals contained therein is disclosed. The process includes the partial roasting of the concentrate to open the pyrite matrix to solution penetration followed by hydrometallurgical steps, including ferric sulphate leaching, reduction leaching, solid-liquid separation and metal extraction steps, to recover the copper and zinc separately and silver in concentrated form.

Abstract: A process for treating a pyrite concentrate containing silver, copper, lead and zinc to recover the metals contained therein is disclosed. The process includes the partial roasting of the concentrate to open the pyrite matrix to solution penetration followed by various hydrometallurgical steps, including oxidation and reduction leaching, solid-liquid separation and metal extraction steps, to recover the copper and silver together, and the lead and zinc separately.

Abstract: Sodium carbonate is crystallized in multi-stage evaporative crystallizers from a pregnant liquor process solution typically obtained by dissolving calcined crude trona in water, separating insoluble impurities, and removing the majority of organic matter with activated carbon. After separation from the sodium carbonate crystals, a portion of the mother liquor usually is recycled to the crystallizers, and the remainder is purged to prevent buildup of impurities. Product quality is improved, and the amount of purged mother liquor is reduced by feeding the pregnant liquor predominantly to the initial stage crystallizers, directing the majority of the recycled mother liquor to a final stage crystallizer, recovering sodium carbonate crystals from slurries from at least the initial stages, and withdrawing purge liquor only from the slurry from the final stage crystallizer.

Abstract: Described herein is a process for producing soda ash (sodium carbonate) from natural ores such as trona in which separate soda ash products are produced having differing purities. According to the invention, a substantially purified and saturated solution of sodium carbonate is divided into at least two separate process streams, one of which is subjected to crystallization in the absence of recycled mother liquor to form high purity sodium carbonate-containing crystals, while the other stream is subjected to crystallization in the presence of recycled mother liquor to form lower purity crystals. The crystals are thereafter separately processed to obtain soda ash products of differing grades.

Abstract: A process for obtaining pure orthophosphoric acid from superphosphoric acid is provided comprising:(a) hydrolyzing superphosphoric acid with water until a mixture of polyphosphoric acids and orthophosphoric acid is formed, wherein the total P.sub.2 O.sub.5 content of said mixture is from 65% to 70% and the poly P.sub.2 O.sub.5 content of said mixture is from 1% to 15% of the total P.sub.2 O.sub.5 ;(b) crystallizing said orthophosphoric acid from said mixture;(c) separating said orthophosphoric acid from said mixture; and(d) washing said orthophosphoric acid with an organic solvent having a low or limited solubility for orthophosphoric acid.