Kinetics of sulfuric acid leaching of nickel from grinding waste of rhenium-containing superalloys

Abstract

The paper studies the kinetics of sulfuric acid leaching of nickel, the main component of grinding waste of ZhS-32VI rheniumcontaining heat-resistant superalloy formed during mechanical processing of products and containing such impurities as abrasive materials, oils, ceramics and other contaminants with refractory metal concentration in a solid residue, in agitation mode. The nickel content is 60 %. In addition to nickel, grinding waste contains other metals such as rhenium, chromium, cobalt, tungsten, tantalum, molybdenum, hafnium, titanium, and aluminum. The process of nickel leaching from waste with a sulfuric acid solution was carried out in a thermostated cell at an elevated temperature (55–85 °С), waste : 3 M H2SO4 solution phase ratio of 1 g : 10 ml, and stirring rate of 200 min–1. Kinetics was studied using a fraction of –0.071 mm with the highest yield (49.2 wt.%) in grinding waste. Convex kinetic curves of nickel leaching from waste were obtained. It was found that when the temperature changes from 55 to 85 °С, the time until leaching stops decreases from 220 to 140 min, and nickel recovery from the solution increases from 45 to 99 %. The data of the obtained kinetic curves were linearized according to the «contracting sphere» equation, Gistling–Braunstein and Kazeev–Erofeev equations (the latter is most suitable for description). Taking into account the assessment of anamorphosis correlation coefficients, it was found that nickel leaching from grinding waste is limited by the chemical reaction, and the process proceeds in the kinetic region of the reaction. The apparent activation energy calculated using the Arrhenius equation and rate constants obtained by processing linearized kinetic curves according to the «contracting sphere» model, was 47.5±0.5 kJ/mol. This value confirms the course of the process in the kinetic region where the process can be intensified by increasing its temperature.