Study On Procedure Toxicity And Harmless Disposal Of Manganese Mine Tailing Slag

In recent years, the processing and recycling of manganese slag becomes anincreasingly serious problem because of the rapid development of manganese industryin China. However, due to the financial shortage and technical limitation, manymanganese enterprises usually directly deposited the manganese slag on the residuefield without any treatment, resulting in serious environmental pollutions.Based on such situation, this article provides an overview of the production statusof current manganese industry and the sources of manganese slag, as well as itsenvironmental hazard and recycling status.The samples in this study is an industrial residue with high moisture, They areproduced in the course of leaching manganese carbonate with sulfuric acid. a typicalmanganese slag in Xiushan District, Chongqing.The manganese slag samples were characterized and analysised by the methods ofX-ray fluorescence spectroscopy （XRF）, X-ray diffraction （XRD）, atomic absorptionspectrophotometry and other modern testing methods. The results show that freshmanganese slag is black mud powder with a moisture content of of27.5%, a density of1.896g/cm³and an average pH value of about5.9. The manganese slag contains theelement of O, Si, S, Ca, Al, Fe, Mn, K, Mg, Na, Zn, Cr, P, Ni, Pb, Cd etc. As the mainelements are shown in the form of oxides, the chemical composition of manganese slagare: silica （SiO₂）, calcium oxide （CaO）, oxide of aluminum （Al2O3） oxide, iron（Fe2O3）manganese dioxide （MnO₂） and sulfur trioxide （SO3）. The total content of Mn in theslag manganese was3.86%, while the contents of water-soluble、 MnCO₃and MnO₂were1.89%1.49%and0.47%, respectively. The particle size of most manganese slagwas lower than180μm, while about79.39%particles was less than180μm in size and66.71%of that was less than147μm, which show that these industrial residues belong tosmaller particls. Additionally, The slag samples contains phases of CaSO42H2O、SiO₂and MnCO₃.The experimental results of leaching toxicity from manganese slag showed that: theconcentration of manganese ions in the leaching solution was1812mg/L, which was906times higher than the effluent discharge standards （2.0mg/L）. And theconcentrations of Zn, Ni, Cd, Pb, Cr did not exceed the standard value determined bythe leaching toxicity identification rules, but they were beyond the maximum emission concentration to be allowed for the pollutants. Moreover, the manganese slag is acidicwith high water content, and the heavy metal ions in it would dissolve and migratebecause of the rain, so the manganese slag without appropriate treatment would beharmful to the environment.The effect of experimental conditions on the leaching result was also analysised.The results show that: the pH value of solution had a significant impact on the leachingresult of manganese slag. The concentration of Mn in the final leached solutionincreased with the decreasing pH value of extracting solution. And as the liquid/solidratio increased, the leaching concentration of manganese would rapidly reduce at thebeginning and then changed slowly. When ratio is higher than10:1, the leaching rate ofmanganese becomes stable. The leaching rate of manganese also increased rapidly withthe temperature rising below60℃, it would just changed slowly after reaching60℃.The molar ratio of H2SO4/HNO3as5:1was used to adjust different pH values tosimulate the acid rain leaching experiments. And the experimental results show that: thedissolved concentration of Mn²⁺become higher with the decreasing pH value ofsimulated acid rain. At the early stage of leaching process, Mn²⁺dissolved sufficiently,but the concentration of Mn²⁺in leachate solution would decrease. The decrease ratewas fast at first and then become slow. The pH value of simulated acid rain also had asignificant effect on the dissolved concentration of Mn²⁺from the manganese slag, andthe lower pH value of extraction solution was benifical to the dissolution of Mn²⁺.According to the manganese slag properties from experimental results, the harmlesschemical method on the processing and utilizing of manganese slag by compositecuring agent was also investigated in this paper. The initial and final solification time ofcement curing body and its compressive strength, as well as the X-ray diffractions ofleaching toxic materials and cured products, were also analysised. The results indicatedthat the leaching toxicity from manganese slag was significantly reduced after processedby the composite curing agent, and the concentrations of heavy metals in the leachingsolution were lower than the limits of the Toxicity Characteristic Leaching Procedure（TCLP） standards for the solid waste, which can effectively control their pollution tosurrounding environment.