Analysis Of Electroplating Sludge Properties And Research On Low Temperature Drying Technology

As an important process for material decoration and protection,electroplating has been widely applied in various industries.According to present data,there are about 200000 electroplating enterprises in China and 12 million tons of electroplating sludge output per year.These industrial solid hazardous wastes are subject to strict control due to the high content of heavy metals,easy diffusion,and difficult remediation.At the same time,the import of metal resources is strictly restricted,so the recycling and utilization of electroplating sludge has become more and more popular in research and actual production.Drying dehydration can reduce and stabilize electroplating sludge,and is also an important process in the recycling and utilization of metals in electroplating sludge.Therefore,the comprehensive energy consumption of sludge drying is the key factor affecting the recycling and utilization of sludge.Electroplating sludge from three electroplating enterprises with obvious differences in average drying energy consumption.Through systematic investigations on the basic components,rheological properties,key parameters of the sludge drying process,and dynamic analysis of the low-temperature drying process of electroplating sludge,the effective water diffusion coefficient and activation energy of the drying process under corresponding operating conditions are obtained,which could provide foundations for the optimization of the low-temperature drying process of electroplating sludge.Based on the analysis of the basic characteristics of electroplating sludge,it is concluded that the three types of electroplating sludge samples are weakly alkaline and non-corrosive,with a lower water content compared to ordinary municipal sludge.The ash content of the three types of electroplating sludge samples is over 75.01%,and the content of C,H,N,and S in the samples is relatively low,indicating that the content of organic matter in the electroplating sludge is relatively low,and there are fewer metals in the form of chelates,most of which exist in the form of hydroxides,among which there are also some sulfides.The metals in the three electroplating sludge samples are mainly Cr,Cu,Ni,and Zn.The maximum values of Cr,Cu,Ni,and Zn measured by ICP-MS are 189.30 mg/g,246.84 mg/g,174.47 mg/g,and 108.85mg/g,respectively.At the same time,the leaching toxicity of Ni,Zn,Cd,and Pb in electroplating sludge samples exceeds the standard,indicating that the three types of electroplating sludge have high recycling value and greater environmental risks.During the drying process of electroplating sludge,the internal water diffusion coefficient of electroplating sludge has an important impact on the drying rate and energy consumption.According to Stokes’law,there is a quantitative relationship between the viscosity of electroplating sludge and the internal water diffusion coefficient of electroplating sludge.Therefore,studying the viscosity of electroplating sludge is of great significance to the drying pretreatment and transportation processes of electroplating sludge.Based on the analysis of the rheological properties of electroplating sludge,it is concluded that electroplating sludge exhibits shear thinning properties,and the relationship between the linear velocity of the rotor and the viscosity of electroplating sludge basically presents a Power equation relationship.In addition to the linear speed of the rotor,the viscosity of electroplating sludge is also related to the type,water content,and temperature of the electroplating sludge.The viscosity of different types of electroplating sludge varies greatly,which may be related to the nature and water content of the electroplating sludge.As the linear speed of the rotor increases,the water content of electroplating sludge increases,and the temperature increases,the viscosity of electroplating sludge decreases.In actual electroplating sludge treatment processes,reducing the viscosity of electroplating sludge can increase its internal water diffusion coefficient,improve drying rate,and reduce energy consumption.Based on this,a systematic study on the inffluences of key parameters,including temperature and relative humidity,on the drying process of electroplating sludge was investigated.Five wildly used drying models were adated to fit the drying process of electroplating sludge.It was found that the Page model had the highest fitting degree to the Dehydration kinetics process of electroplating sludge.The range of effective water diffusion coefficient of electroplating sludge is 2.73×10^-5 m²/s～1.01×10^-4m²/s,the maximum value is reached at 70℃and 40%relative humidity.The drying activation energy of electroplating sludge ranges from 14.90 k J/mol～38.05 k J/mol,and the higher the relative humidity,the higher the activation energy.Through range analysis and variance analysis,the effect of drying process parameters on the drying performance of electroplating sludge was further studied.It was found that the relative humidity of the drying box had a more significant impact on the relative unit energy consumption and average drying intensity than the temperature;The optimal process combination for relative unit energy consumption is temperature 65℃and relative humidity 40%;The optimal process combination for average drying strength is temperature 70℃and relative humidity 40%.Therefore,in the actual drying process of electroplating sludge,it is necessary to control the relative humidity,rather than blindly increasing the drying temperature.