Study On Solidification Of Pollutants In Electrolytic Manganese Slag By Red Mud

Electrolytic manganese residue（EMR）is a kind of solid waste produced in the process of manganese production,which belongs to general industrial solid waste.In this paper,EMR as the research object,red mud,quicklime,etc.as curing agents,to explore the curing effect of different factors（addition amount,reaction time,reaction temperature,liquid-solid ratio）,and the solidification mechanism was preliminarily elaborated,including the following work contents:（1）analysis of the physical and chemical properties of EMR and red mud::（2）exploring the dissolution law of heavy metal ions in EMR::（3）The effect of EMR on the solidification of red mud was studied.Through the research of this paper,the following research results are obtained:1.The p H value of EMR is about 5.73,which is acidic.It mainly contains quartz,gypsum,calcite,Mn SO₄·H₂O,（NH₄）₂Mn（SO₄）₂·6H₂O,Ca Mn₂O₂ and other minerals.The p H value of red mud is 10.23～12.36,which is alkaline.It mainly contains nepheline,plagioclase,perlite,clay minerals,kaolinite,calcite and other minerals.2.The results of EMR leaching toxicity test show that the EMR contains the first kind of pollutants such as Cr,Cd,Ni,Pb and the second kind of pollutants such as Mn,Zn.The concentration of manganese ion in the horizontal oscillation leaching solution is 679 mg/L,and the manganese ion concentration in the overturning oscillation leaching solution is 1200 mg/L（N=6）.The heavy metal concentration in the overturning leaching solution is higher than that in the horizontal leaching 521 mg/L.the p H value is an important factor affecting the dissolution of heavy metals from manganese slag.3.The results of simulated acid rain experiment show that the content of manganese ion is 6056mg/L in the initial stage of leaching.This is because the water-soluble and weakly acidic manganese ions in EMR are more active in water and easy to transfer to the environment.In the middle and late stages of leaching,a large number of soluble manganese ions have been dissolved out,and the reduced manganese ions are slowly dissolved under acidic conditions.The amount of manganese ions dissolved gradually decreases with the increase of leaching time.On the sixth day（1.5 years of simulated acid rain）,the amount of manganese ion dissolved tends to be stable.4.The results of EMR showed that the solidification rate of pollutants in manganese slag was 99.8%.When the initial content of manganese ion is 1208～1611mg/L,the dosage ratio of curing agent is 10%.When the initial content of manganese ion is less than 500mg/L,the dosage ratio of curing agent is 3%-5%.From the perspective of economic cost,the curing effect of red mud as curing agent is further studied.The curing rate of 30%fresh red mud to manganese ion is 93.7%,which can be used as low-cost treatment of EMR.The solidification rate of manganese ion is 58.6%for 30%of old red mud（which has been stacked for more than one year）.When 30%old red mud is combined with low concentration quicklime（1%～2%）,the solidification rate is increased by 25.5%.The results showed that the optimum solidification conditions of compound quicklime from old red mud were as follows:30%of old red mud,5%of quicklime,12h of reaction time,99.8%of soluble manganese ion,and less than 2mg/L of residual manganese ion（1.82mg/l）,which met the requirements of integrated wastewater discharge standard（GB8978-1996）.5.Analysis of solidification mechanism analysis:there are a large amount of soluble Mn²⁺,Ca²⁺,SO4^2-,CO₃^2-,OH^-in the consolidation body of red mud electrolytic manganese slag under the slurry system:under the slurry system,a large amount of soluble Mn²⁺,Ca²⁺,SO₄^2-,CO₃^2-,and OH^-are found in the consolidation body of red mud electrolytic manganese slag under the slurry system.According to the equilibrium constant of precipitation and dissolution equilibrium constant of insoluble matter,the solubility product KS of Ca SO₄=7.10×10^-5,and the solubility volume KS of Ca CO₃=4.96×10^-9,Mn（OH）₂=4×10^-14,K_{（Mn（OH）2）}<K_{（Ca CO3）}<K_{（Ca SO4）},according to the equilibrium constant of precipitation and dissolution equilibrium（NH₄）₂Mn（SO₄）2·6H₂O and Mn SO₄ Manganese ion of 6H₂O reacts with OH^-to form Mn（OH）₂ precipitate firstly.SEM images before and after the solidification of electrolytic manganese slag show that,after adding red mud（new and old）and quicklime respectively,the columnar and strip-shaped particles（Ca SO₄）in the electrolytic manganese slag gradually decrease,which is because Ca SO₄ gradually transforms into Ca CO₃ under the action of OH^-and CO₂,and finally reaches the dissolution equilibrium.