Pyrite Residue Desulfurization Arsenic

Pyrite slag is a kind of waste slag discharged from the process of producing sulfuric acid from pyrite in chemical factory, which contain mainly Fe and a few impurities such as Si, Ca, Mg, S, As, Cu and Ag etc. Its main minerals include hematite, magnetite, quartz, gypsum etc. The amount of pyrite slag discharged is about 1.0×107～1.5×107 t each year. At present a large amount of pyrite slag is stored up or filled in buries processing, not only it occupies plenty of land, but also the factory must pay the expense of the land, the transport expense, the filling spends in buries and so on. At the same time it also does pollution to air, water and earth. Meanwhile there are much Fe, about 40%-60%, and many useful materials such as Cu, Ag, Au in the pyrite slag, and it is a kind of valuable reused resource. Therefore, to reuse the slag not only can eliminate pollution, but also turn waste to useful material which can bring some economic profit and society profit.Comprehensive utilizing pyrite slag has been paid more attention in many countries and many developed countries already have carried on the comprehensive utilization research of pyrite slag many years ago. Although people began to study the utilization of pyrite slag from 1970's in china, because of bad quality of our slag, lower level of technology and lag economy etc, the utilization ratio is still far lower than other countries. There are many difficulties in utilizing the slag, in which the most main one is the impurity of pyrite slag can not be removed of, specially the arsenic element and the sulfur element bring the harm to the comprehensive utilization of slag (such as Fe raw material).This paper researches the process that pyrite slag is leached by sulfuric acid solution, which can remove As and S element in pyrite slag effectively. The research indicates that after the slag is treated with sulfuric acid solution, As content is reduced to 0.036%, it's elimination eficiency is 98.7%, S content is reduced to 0.319%, Fe content of sample treated is raised to 62.56%, and As content and Fe content the in treated slag can satisfy quality achievements of iron-smelting raw material.To obtain optimum process conditions, the paper studied effect of sulfuric acid concentration, temperature, solid concentration, the reaction time, stirring speed on Fe, As and S content of sample, and conduct orthogonal experiment.The optimum technical conditions of removing of As and S are:the concentration of arsenic removal reagent is 15%, the temperature is 50℃, the solid concentration is 30%, the reaction time is 120 minutes, and the stirring speed is 300 rpm.The paper study circulation utilization of the waste liquid obtained from leaching pyrite slag with sulfuric acid by returning to leaching stage. The research indicates that when the waste liquid is returned to the leaching stage to leach pyrite slag, which is matched with acid, free sulfuric acid in leaching liquid can be utilized effectively and the amount of industry sulfuric acid used is reduced obviously. When circulation utilization of the waste liquid reaches three times which is returned to the leaching stage to leach pyrite slag, the As and S content in processing sample may be reduced effectively and the iron is concentrated simultaneously, As and Fe content in sample can achieve the quality requirement of raw material of iron-making.Because S content of sample do not achieve the quality requirement of raw material of iron-making when pyrite slag is leached by sulfuric acid solution, the paper study effect of additive in sulfuric acid solution on removing S from pyrite slag. The research indicates that when K2Cr2O7 or KClO3 is mixed into sulfuric acid solution and the solution is used treating pyrite slag, S content in sample may be reduced to 0.279～0.291%, and can achieve removal of As and S simultaneously. The pyrite slag of removing As and S can achieve the quality requirement of raw material of iron-making.Meanwhile the paper carried on dynamics research of the processing of removing the arsenic element from pyrite slag by sulfuric acid.Simultaneously dynamics research indicated that, the leaching process of removing arsenic from pyrite slag by sulfuric acid may be described by the unreacted shrink core model with solid resultant (inert material) and the invariable particle size, chemical reaction speed of leaching process was controlled by surface chemical reaction process, the chemical reaction apparent activation energy of leaching process Ea=140.075kJ/mol, the chemical reaction order is 0.8287.