Electrolytic Manganese Residue Detoxicification By Calcined Raw Materials

No manganese no steel.Manganese has important strategic significance in the national economy.As the largest electrolytic manganese producer and consumer in the world,China produces more than 95%manganese of the world.The rapid development of electrolytic manganese industry has brought serious environmental pollution,especially the electrolytic manganese residue（EMR）which has become the largest and most dangerous threat in the industry.At present,resource utilization for EMR is still immature,and harmless storage is the preferred way for EMR disposal.The key to achieving harmless storage is the stable solidification of manganese and the removal of ammonia nitrogen.In this paper,EMR discharged from an electrolytic manganese enterprise in Guizhou Province was taken as the research sample,and the harmless treatment of EMR was carried out by using the intermediate product of cement kiln—calcined raw material.The effect of EMR particle size,moisture content,calcined raw material amount and temperature on the solidification of Mn and the removal of ammonia nitrogen in the EMR were studied.The long-term stability of EMR after calcined raw material solidification was studied,and the mechanism of the process was analyzed,and the advantages of the calcined raw material were clarified.This study provides a new method for the harmless treatment of EMR.The main conclusions are as follows:（1）Chemical speciations of various heavy metals in EMR are mainly water soluble and weakly acidic,which are easy to migrate to the environment and ecosystem,resulting in environmental pollution.The leaching toxicity test of EMR showed that Mn²⁺and ammonia nitrogen were the main pollutants.The contents of Mn²⁺and ammonia nitrogen in the leaching solution were 1481.22 mg/L and 680.99 mg/L,respectively,which were 740 times and 45times of the first level of the national wastewater discharge standard（GB8978-1996）.（2）The traditional manganese fixation stabilizer is quicklime,calcined raw material shows a smaller particle size,a larger specific surface area and pore volume than that of puicklime.And the hydration products of calcined raw material are Ca（OH）₂,ettringite(Ca₆Al₂（SO₄）₃（OH）₁₂·26H₂O),gismondite（2Ca O·3Si O₂·H₂O）,etc.,which have good treatment effects on heavy metals.Ca O content and effective Ca O content are lower than quicklime,the effect of calcined raw material to treat EMR is also good,and the p H value of EMR after treatment is in the range of 6-9,which meet the national wastewater discharge standard（GB8978-1996）.（3）The results of harmless treatment of EMR by calcined raw material showed that manganese fixation and ammonia removal effect of EMR was the best when the particle size of EMR was less than 0.15 mm,the moisture content was 25%,the addition amount of calcined raw material was 9%,and the aging temperature was 60 ^oC.After that,the leaching concentration of Mn²⁺was less than 0.02 mg/L and the curing rate was more than 99.9%.The leaching concentration of ammonia nitrogen is 0.68 mg/L,the removal rate of ammonia nitrogen is above 99.9%,and p H value after the treatment is 8.75.The leaching concentration and p H value meet the first level of the national wastewater discharge standard（GB8978-1996）.（4）Through the study of the interface behavior of calcined raw material in the EMR system,it is found that calcium-containing substances are wrapped in the EMR system by the observation of electronic probe and other microscopic testing methods.The main reason is that the alkaline environment formed in the hydration process of burnt raw meal promotes the formation of precipitation of heavy metals.Ca O,Al₂O₃,Si O₂ react with high concentration of sulfate in EMR to generate Ca SO₄,hydrated calcium silicate,ettringite and other substances,which encapsulates and adsorbs heavy metal ions and covers calcium-containing substances,thus forming a stable solidified body.（5）The study on the long-term stability of the manganese fixation system after the treatment of EMR with calcined raw material showed that the long-term stability of the untreated EMR is poor,while the EMR after the treatment of calcined raw material has good long-term stability,since manganese in the EMR is fixed in the form of oxides.The leaching concentration of manganese in each leaching period is lower than 5 mg/L,and the observed diffusion coefficients are lower than 10^-9.