The Migration And Transformation Of Manganese And Ammonia Nitrogen In The Leaching Process Of Electrolytic Manganese Residue

The development of electrolytic manganese industry has produced a large number of electrolytic manganese residue(EMR),which has become one of the urgent problems to be solved in the development of electrolytic manganese industry.At present,a large number of EMR stockpiled has high pollution risk.Rainwater is the main migration power source to control pollutants,which makes EMR form leachate containing pollutants such as high concentration manganese(Mn²⁺),ammonia nitrogen(NH₄⁺-N)in the stacking process,seriously damaging the ecological environment around the residue yard.To study the migration and transformation law of Mn²⁺and NH₄⁺-N in the leaching process of EMR is the key to solve the pollution control of EMR.In view of the above problems,by means of investigation and sampling,indoor experiment and model simulation,this paper systematically studied the change law of physical and chemical characteristics of EMR at different stacking times,and explored the influence mechanism of p H value of leachate and amount of potassium permanganate on the migration and transformation of Mn²⁺and NH₄⁺-N in the leaching process.The main conclusions are as follows:(1)The physical and chemical characteristics of EMR with different stacking time were studied.The results show that the p H,moisture content and conductivity of EMR decrease with the increase of stacking time.The total amount of Mn,Ca,Mg and Se in EMR decreased with the increase of stacking time,and more soluble Mn²⁺,Mg²⁺,Se⁴⁺and NH₄⁺-N were lost.The decrease of Total Mn in EMR is mainly due to rainfall leaching,and the lost Mn is mainly exchangeable and carbonate bound.Se has strong mobility in the process of EMR stacking,and the EMR stored for 10 years still has a great risk of environmental pollution.Mn²⁺and NH₄⁺-N in EMR with different stacking time mainly exist in(NH₄)₂Mn(SO₄)₂·6H₂O,(NH₄)₂SO₄,Mn SO₄·H₂O,Mn CO₃,Mn₂O₃,Mn O₂and other phases.In addition,with the increase of stacking time,the average pore size of EMR decreases,the staggered wrapping phenomenon of massive,columnar shaped EMR particles increases,the specific surface area increases,and there are chemical transformations such as catalysis,adsorption and oxidation in the stacking environment.(2)The migration law of Mn²⁺and NH₄⁺-N in EMR under the conditions of p H value of leaching solution and amount of potassium permanganate was studied.The results show that the release of Mn²⁺and NH₄⁺-N in the dynamic leaching process has two stages:rapid leaching and slow leaching,and the cumulative release process conforms to the second-order kinetics.The release of Mn²⁺,NH₄⁺-N and Mg²⁺has a response relationship and positive correlation in time series.The loss of Mn²⁺and NH₄⁺-N in the leaching process mainly comes from the sulfate double salt in the EMR.The order of cumulative release of Mn²⁺and NH₄⁺-N after leaching at different p H is p H=2>p H=4>p H=5>p H=8>p H=9>p H=10,the order of cumulative release after leaching with different amounts of potassium permanganate was 50g<45g<35g<25g<15g.After 50g leaching,the cumulative maximum release of Mn²⁺and NH₄⁺-N was 7050.4 mg·kg^-1and 3130.9 mg·kg^-1,which decreased by about 19.4%and 45.4%compared with 8752.4 mg·kg^-1and 5734mg·kg^-1of 15g,and 23.4%and 29.3%compared with 9200.2 mg·kg^-1and 4426.1 mg·kg^-1of p H=10.(3)The migration and transformation mechanism of Mn²⁺and NH₄⁺-N in leaching process was studied.The results show that Mn²⁺and NH₄⁺-N migrate and transform in the alkaline leaching process.Mn²⁺mainly reacts with OH^-to form Mn(OH)₂.Mn(OH)₂is oxidized to form manganese oxides(Mn OOH,Mn O₂,etc.)and retained in EMR.NH₄⁺-N is mainly trapped in EMR through electrostatic and ion exchange.KMn O₄accelerated the migration and transformation of Mn²⁺and NH₄⁺-N,and Mn²⁺was mainly transformed into new ecological hydrated Mn O₂.The new ecological hydrated Mn O₂adsorbs Mn²⁺and then oxidizes it to form a new active manganese oxide,thus forming a self catalytic oxidation reaction system of manganese.In addition,in the KMn O₄system,Mn on the surface of EMR mainly exists in the form of Mn³⁺,and the manganese oxide formed by manganese autocatalytic oxidation mainly exists in the EMR system in the form of iron manganese oxidation and residue.After leaching,the leaching toxicity of Mn²⁺and NH₄⁺-N in EMR is very low,and the Mn²⁺and NH₄⁺-N that have migrated and transformed are relatively stable in EMR.