Study On The Occurrence And Release Characteristics Of Heavy Metals In Ceramsite Fired From Electroplating Sludge

The amount of electroplating sludge produced in China is large and shows an increasing trend.The use of electroplating sludge to prepare fired building materials products can better realize resource utilization,which is an important potential way of disposal and utilization.However,electroplating sludge usually contains high content of specific heavy metals,which may be released to the environment in specific exposure scenarios.At present,the heavy metal content and leaching characteristics of ceramsite fired from electroplating sludge have been reported.However,the occurrence characteristics of heavy metals in different ceramsites and their leaching effects are not well understood,especially the release risk in practical application exposure scenarios is still unclear.Therefore,this paper investigates the occurrence characteristics of heavy metals in various ceramsite products fired from electroplating sludge,and studies the leaching characteristics of heavy metals and the influence of main factors;Based on the actual application,the typical exposure scenarios were determined,and the long-term release law and environmental risk of heavy metals in ceramsite were studied,so as to provide scientific basis for the environmental risk control of heavy metals in ceramsite products fired from electroplating sludge.The physicochemical properties,content levels of seven heavy metals and leaching characteristics of ceramsite produced from electroplating sludge in China were studied.The results demonstrate that the main chemical compositions of ceramsite fired by electroplating sludge are SiO2,Al2O3,CaO and Fe2O3,and quartz and plagioclase are the main phase composition.The average contents of Cr,Ni,Cu,Zn,As,Cd and Pb in the ceramites prepared by electroplating sludge were 9342,8234,7069,25676,331,9.87 and 275 mg/kg,respectively.At present,there is no corresponding environmental standard for its leaching in China.According to the Technical Specifications for Cooperative Disposal of Solid Waste in Cement Kiln(GB30760-2014),all heavy metals except Ni are lower than the corresponding leachable limit.At the same time,the results show that the cement mortar leaching method is more effective than the sulfuric acid and nitric acid leaching method in characterizing the metal release under strong conditions.The leaching rate of the seven heavy metals is low,which indicates that the high temperature sintering process has a strong solidification effect on the heavy metals.The effects of different factors on the release of heavy metals in ceramsite fired from electroplating sludge were studied.The results showed that the contents of Cr,Cu,Zn and As were significantly different with different ratios of H2SO4:HNO3.Under acidic conditions,the leaching amount of Cr remained at a relatively low level;The leaching amounts of Ni,Cu,Zn and As remained relatively high under acidic conditions.The contents of Cr,Ni,Cu,Zn and As were significantly different under different liquid-solid ratios.The results show that carbonation has a great influence on the release of As in ceramsite,and the leaching amount of Cr,Ni,Cu and Zn has the same trend with the pH of leaching solution.The results of flume experiments showed that there was no significant.difference.in the cumulative release of heavy metals between ceramsite with particle size of 5-10 mm and 20-25 mm.The release and environmental risk of heavy metals in ceramsite under typical exposure scenarios were studied.According to the research results and the actual situation,the experimental parameters were determined to simulate the typical application scenarios:pH=3.2(HNO3:H2SO4=1:2,mass ratio);The liquid-solid ratio was 40 L/kg;The leaching method is continuous leaching.The results show that Ni,Cu,Zn and Cd conform to the one-dimensional diffusion model proposed by Crank,and Cr,As and Pb conform to the second-order kinetic equation.The release mechanism of Cr,As and Pb is surface erosion,while the release mechanism of Ni,Cu,Zn and Cd is diffusion.The exposure of heavy metals in ceramsite fired from electroplating sludge was 2.49×10-4 to 0.965 mg/kg-d.The total cancer risk was 4.87×10-7 and the total non carcinogenic risk was 2.79×10-2,both are acceptable levels.