Experimental Study On The Pretreatment Of Cement Kiln Co-processing Of Gold Mining Waste For Mercury Removal

The native metallurgical process represented by using mercury was widely adopted by small workshops in the early 21st century due to its low cost and easy to operate.With the increase in environmental protection awareness and government supervision,this process has been banned,but the resulting accumulation of gold mining waste poses a serious threat to the surrounding ecology and human health.cement kiln co-processing hazardous waste has attracted people's attention because of its advantages such as large processing capacity,low secondary pollution,and the realization of waste recycling and harmlessness.However,the high mercury concentration of the gold mining waste has become a factor that restricts co-processing,so it is necessary to preprocess the gold mining waste to remove mercury.This paper aims at the heavy mercury-contaminated gold mining waste produced by using mercury in a county in Shanxi province,and conducts an experimental study on the pretreatment of mercury removal before co-processing using cement kilns.This paper first analyzes the physical and chemical properties of the gold mining waste collected on-site,and simulates the pretreatment of using the cement kiln high temperature flue gas to remove mercury,explore the effects of temperature,time,flow rate,size,and atmosphere on the thermal analysis process,analyzed the total mercury content and mercury form of the samples before and after treatment,according to the pretreatment process conditions,design the pretreatment process flow and study the influence of different dosing points on cement clinker.The results obtained are as follows:The mercury concentration in the gold mining wasteranges from 142 mg/kg to 700mg/kg,and 640 mg/kg is taken as the total mercury concentration.The optimized continuous extraction method was used to analyze the form of mercury.The results showed that residual mercury was the main form of the gold mining waste,accounting for 46.01%of the total mercury,followed by organically bound mercury 32.35%,acid-soluble mercury 8.47%,exchange mercury 5.3%,alkali-soluble mercury 4.84%and water-soluble mercury 3.04%.The main mineral phases are silica and calcium sulfate,which can be used as alternative raw materials for co-processing in cement kilns.At 200??800?,as the temperature increases,the mercury removal rate increases,indicating that temperature has an important influence on the pyrolysis effect;above 500?,the mercury removal rate is 95%under different pretreatment times.the time has no significant influence on the mercury removal effect,and Hg⁰is the main existing form in the pyrolysis gas;At 200??400?,the removal rate of mercury in the first 20 minutes changes significantly,and time affects the effect of mercury pyrolysis.Hg²⁺is the main form of pyrolysis gas.Under the condition of 300?,with the increase of time,the content of mercury in each form shows a downward trend.The percentage of organically bound forms first increases and then decreases,and the percentage of residual forms rises.the percentage of acid-soluble,exchangeable,and water-soluble forms drops.At 20 minute,with the increase of temperature,the content of mercury in various forms decreased,and the removal effect of organically bound mercury was the most obvious,the proportion of alkali-soluble mercury increased,and the proportion of other forms remained unchanged.Under the pyrolysis conditions of 300? and 20 minute,the removal effect is best when the flow rate is 300 m L/min.As the flow rate increases,the extraction amount of various forms of mercury first decreases and then increases.The percentage of acid-soluble and exchangeable mercury has increased,while the organically bound mercury has decreased;The particle size has no effect on the removal and form of mercury;the alkaline atmosphere is conducive to the removal of mercury,the effect is best when p H=9.The mercury concentration after pyrolysis is 15.83 mg/kg,and the removal rate is 97.64%.Under alkaline conditions,there is conducive to the removal of organically bound mercury;adding kiln ash has no effect on mercury removal,but kiln ash will inhibit the effect.Design the gold mining waste pretreatment process to removal mercury,using high-temperature flue gas,which mainly includes the pre-treatment stage,thermal analysis stage,gold mining waste residue disposal stage,mercury vapor condensation and tail gas treatment stage.This study simply simulates cement production by using pretreated gold mining waste as an alternative raw material,in order to observe the effect of different temperature dosing points on cement clinker,the results show that the dosing point has no effect on the leaching toxicity of cement,and the cement microstructure added in the low temperature section is more compact.