Reduction of potassium cyanide usage in a consolidated industrial process for gold recovery from wastes and scraps

The main purpose of the present work is to improve the understanding of an industrial process that exploits the synergic action of cyanide ion and three-nitrobenzene-sulphonate for the selective removal of precious metals from various matrices. It has been observed that the cyanide dissolves first gold from the surface, forming dicyanoaurate gold complexes, but this reaction alone is not sufficient to dissolve gold with the observed velocity. A deeper knowledge of the chemical mechanisms can potentially improve the process competitiveness. Important reaction factors have been identified and analyzed. It has been demonstrated that the cyanide amount presently utilized is excessive. Possible reduction products have been also identified. The results can help the search for cyanide reduction and substitution. Yield and velocity optimization, together with a solution toxicity reduction can pave the way to eco-friendly processes for the leaching of noble metals

How to Efficiently Produce Ultrapure Acids

Subboiling distillation has been used since two decades for the purification of analytical grade acids from inorganic contaminants and demonstrated an efficient method to obtain pure acids starting from reagent grade chemicals. Nevertheless, the effect of the subboiling parameters on the purity of the distilled acids has never been methodically investigated. Aim of the present research is a systematic evaluation of the subboiling distillation protocol for the production of pure hydrochloric and nitric acid. In particular, the effect of the subboiling temperature and the number of subsequent distillations was investigated as these parameters were recognised as the most important factors controlling acid purity, acid concentration, and distillation yield. The concentration of twenty elements in the purified acids was determined by Inductively Coupled Plasma-Mass Spectrometry. As a result, the subboiling temperature (up to 82°C) and the number of subsequent distillations (up to four) were demonstrated not to affect the purity of the distilled nitric and hydrochloric acids. Under normal laboratory conditions, the residual elemental concentrations were in most cases below 10 ng/L in both nitric (2.75% w/w) and hydrochloric (0.1 M) blanks. Ultrapure nitric and hydrochloric acids could accordingly be produced under the most favorable conditions, i.e., the highest temperature and one distillation process only