Recovery Of Silver, Copper And Zinc From Sintering EAF Dust

As one of the iron and steel solid waste, the EAF dust (hereinafter referred to assintering ashes) is derived from the flue gas collection of electrostatic precipitator inthe technological process of sintering in iron and steel production. Sintering asheshave complex chemical compositions, except iron, some of which contain harmfulelements such as potassium, copper, zinc and lead together with precious metals silver.In this paper, based on the analysis in physical and chemical properties of sintered ashand previous related techniques to the research subject, a new technology for wetrecycling of sintered ash was developed, which recovering silver, copper and zinc byammonia leaching process.Basic research on physical and chemical properties of sintered ash showed that,silver in the dust exist mainly in the form of AgClO2and AgCl, and the averagecontent of silver is384.3g/t. Zinc in the dust exist mainly in the form of ZnCl2, andthe average content of zinc is1186.7g/t. Copper in the dust exist mainly in the formof CuCl and CuO, and the average content of copper is0.19%. Particle size analysisof sintered ash showed that, the median diameter of1#,2#,3#sintered ash were39.84μm,23.84μm and18.34μm. The specific surface area of1#,2#,3#sintered ash were19.6m2/g,15m2/g and17.5m2/g. Combined with the previous related research,decided to recovering silver, copper and zinc by ammonia leaching process afterwater washing.The experimental study on water washing showed that,64percent of the zinccould be removed after1hour, but the content of silver and copper basically remainunchanged. In the single factor study of ammonia leaching experiment, it is concludedthat the optimum experiment condition were as follows: ammonia concentration14percent, mixing time20min, stirring speed120rpm, leaching temperature30℃,solid-liquid ratio1:1.5. In this condition, the leaching rate of silver, copper and zincwere77.07%,71.25%and42.9%. In addition, the leaching rate is proportional to thecontent of silver, copper and zinc in sintered ash.Firstly, using aldehyde to get silver by reduction reaction, reoccupy zincreplacement to copper elemental, then adding carbonate to get precipitation of zinccarbonate, finally get zinc oxide by calcinating zinc carbonate. In accordance with theabove steps, it could recycling silver, copper and zinc from sintered ash progressively. In the reduction reaction experiment with aldehyde, methanal proved to be the bestreducing agent, and the optimum experiment condition were as follows: reductiontemperature80℃, reduction time10min, methanal concentration40percent,methanal addition2mL/1g(silver content). In this condition, the recovery rate ofsilver could achieve96.38percent and total recovery rate could achieve74.28percent.In the process of zinc replacement to copper, the recovery rate of copper couldachieve70.7percent and total recovery rate is50.4percent. In the experiment ofrecovering zinc, the recovery rate of zinc could achieve61.7percent and totalrecovery rate is26.5percent. In addition, the purity of ZnO product could achieve95.7percent, which is conform to the requirements of industrial production.The overall process of recovering silver, copper and zinc test showed that, thetotal recovery rate of silver, copper and zinc could achieve70.1%,49.4%and45.3%,which is proved the feasibility of this process. According to preliminary estimates, theannual output value of this process could achieve33.64million, which is indicate thehighly economic benefits of this process.