Metal Recovery And Heavy Metals Migration Characteristics Of Ferritic Stainless Steel Picking Sludgy Reduced By Municipal Sludge

Stainless steel pickling sludge as one of the industrial hazardous wastes riches in many valuable metals including Fe and Cr.Using municipal sludge as reducing agent to reduce stainless steel pickling sludge has the characteristics of abundant raw materials,low cost,and co-processing of pollutant emissions.This new method is beneficial to the efficient utilization and resource recovery of municipal sludge and stainless steel pickling sludge.Through waste recycling and clean production,it can realize the unification of economic,environmental and social benefits.This study has launched its work from the following two aspects:（1）study on the recovery characteristics of valuable metals from stainless steel sludge reduction by municipal sludge blended with magnetic separation;（2）study on the heavy metal migration law during the reduction reaction.The recovery characteristics of valuable metals from stainless steel sludge in magnetic separation of municipal sludge reduction were studied in a fixed bed reactor and magnetic separation device.The results show that the reduction and recovery of valuable metals in ferritic stainless steel pickling sludge can be realized by using municipal sludge as reducing agent.Under the optimized conditions,the recovery rate of total metals can reach 61.3%,among which the recovery rates of iron,chromium and nickel are 70.1%,53.7%and 60.3%,respectively.When the reaction temperature is lower than 650℃and the amount of municipal sludge is less than 5%,the recovery rate of metals in pickling sludge will increase with the increase of the two.When the reaction temperature exceeds 650℃and the amount of municipal sludge is higher than5%,it will be beneficial to the deep reduction of pickling sludge and reduce the metal recovery.The carbon dioxide atmosphere is beneficial to improve the recovery rate and yield of pickling sludge.When the reaction time is 5 min,compared with pure N₂atmosphere,adding 50%CO₂ can improve the recovery of concentrate by about 63.5%.According to the migration degree of heavy metals in the reduction process,the main heavy metal elements Cr,Mn,Ni,As,Cd,Cu,Pb and Zn in the two kinds of sludge are divided into three categories by ICP analysis,among which 90%of the nonvolatile heavy metals（Cr,Mn and Ni）are enriched in the slag.The mobility of semi-volatile heavy metals（Zn,Cu and Pb）in the range of reaction temperature generally shows an upward trend ranging from 20%to 60%.The mobility of volatile heavy metals（As and Cd）usually ranges from 40%to 80%.The results of SPSS analysis show that under the appropriate reaction temperature conditions,the order of the significant degree of influence on the valuable metal components in the concentrate is that municipal sludge addition>reaction temperature>reaction atmosphere.The valence state of valuable metals Cr and Fe will change during the reduction reaction.Municipal sludge can reduce Cr⁶⁺in stainless steel pickling sludge to Cr³⁺and Cr 0,which significantly reduces sludge toxicity.