Research On The Efficient Recycling Of Electrolytic Manganese Dioxide Slag

Electrolytic Manganese Dioxide Slag?EMDS?is a solid waste obtained after the reaction of manganese ore powder and sulfuric acid.At present,EMDS lacks efficient means of harmless utilization,leading to the accumulation of EMDS.While the accumulation of EMDS takes up a lot of land resources,it also causes serious water,soil and gas pollution.Therefore,exploring an efficient method for large-scale reuse of EMDS is conducive to solving the problem of environmental pollution and saving disposal costs for enterprises.In this study,the basic physical properties,phase composition,and soluble substances of EMDS were systematically studied.On this basis,the possibility of preparing calcium sulfate whisker and sulfur-oxygen magnesium cementing material by EMDS was explored.The results obtained are as follows:?1?Directly using EMDS as raw material,making full use of the existing magnesium sulfate and manganese sulfate in EMDS and adding an additional amount of manganese sulfate,columnar calcium sulfate hemihydrate can be prepared.The characteristics of the synthesized columnar calcium sulfate hemihydrate were characterized by XRD,SEM-EDS and DTA-TG methods,and the influence of water-to-material ratio,hydrothermal time,hydrothermal temperature,H₂SO₄ mass fraction,manganese ion and magnesium ion on the aspect ratio of columnar calcium sulfate hemihydrate was explored.The study found that columnar calcium sulfate hemihydrate with an aspect ratio of 12.67 can be prepared by using EMDS as a raw material,in which the mass ratio of the magnesium sulfate to the sulfate-removing EMDS is 0.072 and the mass ratio of manganese sulfate to the sulfate-removing EMDS is 0.09.XRD and SEM-EDS analysis results showed that magnesium ions and manganese ions are adsorbed on the surface of columnar calcium sulfate hemihydrate,inhibiting the growth of columnar calcium sulfate hemihydrate in the b-axis direction,thereby promoting its growth in the c-axis direction.DTA-TG thermal analysis results showed that the conversion rate of calcium sulfate dihydrate to?-type calcium sulfate hemihydrate is about 97.59%.?2?Light-burned magnesium oxide and magnesium sulfate heptahydrate were used as raw materials to prepare sulfur-oxygen magnesium cementing material,and the influence of the molar ratio of Mg O:Mg SO₄:H₂O on the properties of sulfur-oxygen magnesium cementing material was explored.The study found that when the molar ratio of Mg O:Mg SO₄:H₂O is 8:1:12,the performance of sulfur-oxygen magnesium cementing material is good.On this basis,EMDS was directly used as the raw material to produce sulfur-oxygen magnesium cementing material by making full use of the soluble magnesium sulfate in EMDS.The magnesium sulfate required for sulfur-oxygen magnesium cementing sulfur-oxygen magnesium cementing material was explored.The results showed that the incorporation of Mn²⁺is beneficial to the performance improvement of the magnesium oxysulfide cementing system.With the existing manganese sulfate in EMDS,cementitious materials with 28d compressive strength of 11.3MPa and softening coefficient of 0.83 can be prepared by adding an appropriate amount of manganese sulfate to get the mass ratio of manganese sulfate to magnesium oxide of 12%.Finally,the influence of modifiers on the properties of sulfur-oxygen magnesium cementing material was explored.The results showed that among aluminum dihydrogen phosphate,citric acid and EDTA,the modification effect of citric acid is the best.while the mass ratio of citric acid to magnesium oxide is 1%,the compressive strength of sulfur-oxygen magnesium cementing material is 15.5MPa and the softening coefficient is 0.93.