Theory and experiment of purifying ruthenium-salt & preparation of high-purity ruthenium-powder

Ruthenium refining process could be divided into two steps which were purification of ruthenium salt and preparation of high-purity ruthenium powder. In this paper, the necessity and feasibility of separation osmium and ruthenium from each other by selective oxidation and vacuum distillation divided into two steps were analyzed theoretically, based on the redox standard electrode potential as a criterion of the selective oxidation separation for osmium and ruthenium. The first step was separating osmium oxidized from ruthenium hydrochloric acid absorption liquid by H2O2selective oxidation and vacuum distillation, in which ruthenium was not oxidized and still in ruthenium hydrochloric acid distillation-residue. Osmium tetroxide (OsO4), which formed in the process of oxidation and vacuum distillation, was absorbed in sodium hydroxide solution. And the second step, which was separating ruthenium oxidized and residual osmium oxidized from the first step's residue by oxidation and vacuum distillation with the addition of H2SO4and NaClO3, were studied. Ruthenium tetroxide (RuO4), which formed in the process of the second step, was absorbed in hydrochloric acid solution and purified ruthenium hydrochloric acid absorption liquid was gotten. Pure ruthenium sulfide crystals could be obtained by crystallizing and precipitating the purified ruthenium hydrochloric acid absorption liquid with sodium sulfide, and all kinds of phenomena in the process were explained in theory. Sponge ruthenium powder was prepared by sintering the resultant ruthenium salt under the optimum operation condition of the sinter and reduction in hydrogen atmosphere. The sponge ruthenium powder was washed first by a mixed solution of aqua regia and hydrofluoric acid, and further washed by water before drying. The purity of prepared ruthenium powder was at least 99.995% excluding the gaseous ingredient elements analyzed by glow discharge mass spectrometry(GDMS), and could be used for preparing high-purity ruthenium sputtering target. This study provides the theoretical and experimental basis for industrialized production of high-purity ruthenium powder with purity of 5N(99.999%). © Editorial Office of Chinese Journal of Rare Metals. All right reserved.