Typical Contaminants’ Characteristics And Prevention In The Zinc Hydrometallurgy

Environmental pollution was a key problem that restricted the sustainable development of lead-zinc smelting industry.This paper had taken the conventional leaching process of zinc hydrometallurgy as the research object,to analyze and study the migration and transformation of heavy metal elements,pollution characteristics of produced pollutants and potential risks of pollutants in the production process for the first time.The research results can provide quantitative data support for improvment resource utilization,energy conservation and emission reduction level,hazardous waste management and accurate formulation of pollution prevention and control countermeasures.（1）According to the present situation of production in a conventional zinc hydrometallurgy enterprise,the materials balance and pollution production of the production system had been calculated and analyzed by the method of material flow and production data of environmental engineering.For each treatment of 1 t zinc concentrate,4141.56 m³of air was needed to be consumed.All kinds of waste residue414.99 kg,zinc ingot 471.94 kg,sulfuric acid（93%）820.59 kg were produced.The metal recovery of Zn was 94.54%,and its main loss were 1.43%in copper cadmium slag and 2.21%in kiln slag.（2）The main pollution sources of conventional zinc hydrometallurgy process were identified,which mainly included leaching residue,copper cadmium residue,cobalt residue,anode mud,zinc scum,kiln slag,gypsum residue,zinc powder slag,lead mud,flotation silver concentrate,dirty acid,final drainage and unorganized dust.On this basis,the phase,leaching toxicity and corrosiveness of the typical solid waste residue were analyzed,and the pollution characteristics were determined.The results showed that the pollution characteristics of different solid waste residue had certain differences.（3）Using BCR step-by-step extraction method,the Pb、Zn、As、Cu、Cd、Sb、Ni、Co、Ag and other elements in solid waste residue produced by different sewage nodes were analyzed.The potential harmfulness of heavy metals in solid waste residue were studied by combining the data of transfer coefficient,potential transfer coefficient and harmless coefficient.The results showed that the harmfulness of heavy metals in different waste residue were different.By data analysis method which combined the data of transfer coefficient,potential transfer coefficient and harmless coefficient.a.In the zinc leaching residue,silver concentrate and gypsum residue,all the heavy metal forms of zinc and cadmium were mainly in the form of acetic acid extractable,which mainly existed in Zn O,Cd O and Zn SO₄.In rain or long-term natural stacked,they were highly mobile than other heavy metals,greater harm to the environment;As was stably present in the residue state,and its harmlessness coefficient was above 80%,which was less harmful to the environment.b.In copper-cadmium residue,the Co、Cd、Ni、Zn mainly existed in the form of acetic acid extractable state and the easy transfer coefficient were above 60%,which migrated easily into the environment.Although the total content of Cu was the highest,it will migrate to the environment in large quantities only when the external environmental p H value and oxidation potential change.In cobalt residue,the Zn、Co were easy to migrate to the environment,while As 94.27%was stable in the residual state,which was harmless to the environment.c.The total content of Zn、Pb in anode mud were the highest,which were30840.00、31920.00 mg/kg respectively.Among them,Zn mainly existed in the extractable state of acetic acid,and its easy transfer coefficient was as high as 86.73%,which had high mobility,the Pb was mainly in the Pb SO₄、Pb Mn₈O₁₆mineral phase,and its transfer coefficient was only 0.03%,which was relatively stable.The Zn in zinc slag was mainly in the form of Zn O,which was easy to migrate to the environment.Most of the heavy metals in the kiln slag stably existed in（Fe Mn）₂Si O₄,Ca₂Si O₄and other silicate mineral phases,or mostly existed in the form of sulfide,with relatively low transfer coefficients and relatively small potential environmental hazards.The total content of Pb in lead mud was the largest,but the easy transfer coefficient was the lowest.The heavy metals in zinc powder furnace ash were less harmful to the environment.（4）The potential ecological risk index（RI）evaluation method,Nemero comprehensive index method and human health risk evaluation method were used to evaluate the risk of hazardous waste residue,waste water and unorganized dust,respectively.The results showed that kiln slag and zinc powder furnace ash had the lowest potential harm to the environment;zinc leaching residue,silver concentrate,copper cadmium residue,cobalt residue,anode mud,gypsum residue and lead mud all had very high Zn、Cd pollution risk to the environment;waste water from sewage entry port was mainly affected by heavy metal Zn、Cu、As and suspended matter SS.Unorganized dust produced in zinc smelting process had a non-carcinogenic health risk to human body,and the dust ingested by respiratory system played a decisive role in the non-carcinogenic risk to human body,among which Pb,Cd,As and other elements were the key risks of non-carcinogenic risk to human body.