Study On Reinforced Acid Leaching Of Ferric Iron In Pyrite Cinder

Pyrite cinder is a kind of industrial solid waste, which contains toxic/hazardous heavy metals with potential environmental risks for disposal. Meanwhile, it also contains significant recyclable resources, mainly iron oxide. In this study, for the environmental protection and resources recycling, new extraction means of iron in pyrite cinder, reductive acid leaching are presented, by integrating the technology trend of comprehensive utilization of pyrite cinder and learning the experiences of extraction means of iron in the cinder. The purpose of this paper is to provide new effective way for the treatment and utilization of the cinder.In this paper, the sample of pyrite cinder was collected from a smelter company located in Hunan province, China. The cinder is the sulfating roasting residues of gold-bearing pyrite. The physical characteristics and chemical properties of cinder sample were analyzed by XRD,SEM-EDS and ICP. The results showed a high total iron content of 40.25% in the pyrite cinder, with over 98% occupied by ferric iron, which brought a big difficulty for direct leaching with sulfuric acid solution. Experimental studies were carried out from the following aspects:(1) The research for technology conditions of sulfuric acid leaching of iron with sulfide as additives. (2) Kinetics study of the reductive leaching. (3) Study on recovery of sulfur from sulfurated leaching residues.The reductive leaching of iron with sulfide as additives was in sulfuric acid solution, and it was carried out in normal and pressor atmosphere respectively through condition tests and orthogonal tests. Effects of the following factors on leaching have been studied, there are:the dosage of additives, sulfuric acid consumption, initial sulfuric acid concentration, liquid-solid ratio, reaction time, reaction temperature and stirring speed. The additives are mixtures composed of 50% ZnS,25% Na2S,20% MnS,4% CaS,0.5% Na2S2O3·5H2O,0.5%C3H3N3S3.The results are as follows. Firstly, in normal atmosphere, the iron leaching rate reaches over 89.2%, and the zinc leaching rate reaches 89.2% on the following conditions:leaching agent/slag (g/g)=0.69, surplus coefficient of sulfuric acid is 1.4, liquid-solid ratio=2:1, stirring rate is 1300r/min,95℃,2h. The sequence of impact extent is that the dosage of leaching agent>reaction time> sulfuric acid consumption>reaction temperature. The SEM and XRD analyses of the leached sample indicate dramatically changed and smaller particle size of the cinder sample and the presence of rhombic sulfur. Secondly, in pressor atmosphere, the iron leaching rate reaches 99.4%, and the efficiency of use of additives reaches 98.9% on the following conditions:surplus coefficient of leaching agent is 1.1, surplus coefficient of sulfuric acid is 1.4,3.5M initial sulfuric acid concentration with 800r/min stirring rate,95℃,3h. The sequence of impact extent is that sulfuric acid consumption> reaction time> the dosage of leaching agent> reaction temperature.The kinetics aspects of the reductive leaching of ferric iron in pyrite cinder were investigated. The effects of reaction temperature, initial acid concentration and the additives concentration were determined. The shrinking core model with diffusion control fits the experimental results well and the reaction rate is controlled by diffusion through the product layer. The kinetic model is 1-2/3(X)-(1-X)2/3=92.8e(-4078.8T)t, and the leaching rate formula is (?)The results showed a reaction order of 1.2485 for sulfuric acid and 0.3021 for the leaching agent concentration. The scanning electron microscope (SEM) and energy dispersive spectrum (EDS) analysis indicated that both the sulfur and gangue mineral played the product layer.The recovery of sulfur with ammonium sulfide from the leached residues was studied. Effects of the following factors on recovery of sulfur were studied, there are:ammonium sulfide concentration, liquid-solid ratio, dissolving temperature, dissolving time, thermal decomposition temperature, thermal decomposition time. The results indicated that the dissolution rate of sulfur reached 97%, and the sulfur exhalation rate reached over 99% on the following conditions: ammonium sulfide concentration was 1.17 mol/L, liquid-solid ratio was 10ml/g in a temperature of 25 degrees for 5min, and the thermal decomposition was carried out in 100℃for 120min.