Study On The Pretreatment Process Of High Fluorine And Chlorine Containing Zinc Fume

The raw materials of high grade mineral are decreasing by exploitation of resources.On the other hand,the demand of social development for resources is increasing which makes people focus on resource recycling.Zinc ash is an important secondary resource on zinc metallurgy,however,due to different sources of zinc ash often has complicated composition.The direct leaching of high fluoride chloride zinc dust produces a large amount of fluoride,chloride ion which has important influence on electrolytic zinc process,so most enterprises will be pretreated.In this paper,we propose a two-step process to treat high fluorine chloride zinc dust.The first step is performed by leaching chlorine with sulfate and modified calcium salt.It dissolves majority of chloride ions and a small amount of free fluorine from the zinc dust.The second stage performs acid leaching of chlorine elution slag to leach zinc and fluorine It provides reference for industrial application by systematic experiment.Though the leaching test of lead chloride,We get the following results:it will have best lead chloride leaching effect when the reaction time is 1 h,the temperature is 70 C;and the amount of sulfate added is 5g/L more than the theoretical amount Under the above conditions,the chloride concentration in the chlorine elution solution can reach 30-40g/L,and the chlorine ion content in the residue can be less than 0.03%;In addition,when the solution contains fluoride ions,chloride ions are removed by sulfate conversion.The chlorine content of the residue increases further as the fluoride ion concentration increases,the results show that the chlorine,fluorine,and lead ions in the slag formed PbCIF,which affected the removal of chlorine.The sulfate and modified calcium salt method can effectively destroy the insoluble substances of PbC1F,and the chlorine content of the residue can be significantly reduced.Based on the results of the above experiment,we conducted tests to remove chlorine and fluorine from various actual high-chlorine and fluorine fumes.We have the following results.Neutral leaching conditions were as follows:temperature 70 C.reaction time 1h,liquid to solid ratio 5:1,the amount of sulfate added was 0.8 times the theoretical amount,and the amount of modified calcium salt added was 1.5 times the theoretical amount.For high-chlorine,low-fluorine dust,the fluoride ions and chloride ions content in the slag is less than 0.1%.For high fluoride chlorine zinc-containing soot,chloride ion leaching rate is about 83%while the fluoride ion concentration is controlled below 50mg/L.Acid leaching and neutral leaching are carried out on the chlorine elution slag,residual acid concentration after acid leaching 15g/L.Neutral leaching pH is around 5.0.At this time,the fluoride ion concentration in the solution is about 3.6g/L,the chloride ion concentration is about 800mg/L,and the fluorine ion concentration in the solution after fluoride removal is about 300mg/L.about 90%of fluoride removal efficiency.The leaching rate of two stages of leaching zinc can reach about 90%Compared with the alkaline leaching method,this process saves the cost of the alkali consumption and better realizes the recovery of zinc in the high-chlorine and fluorine fumes.