Study On Adsorption Characteristics Of Heavy Metals From Wastewater Treatment Residuals

With the acceleration of urbanization,soil environmental security and heavy metal pollution in water are attracting more and more attention.The high toxicity of heavy metals and their accumulation in organisms cause serious effects on the environment and organisms.Al-WTR has the characteristics of well-developed pores,large specific surface area and more alumino-oxygen compounds,which has the potential performance as a cheap and efficient adsorbent.The use of wastewater treatment residuals as an adsorbent to remove heavy metals can not only control the heavy metal pollution in the soil and water environment,but also solve the problem of sludge disposal.Due to the difficulty in degradation and accumulation of heavy metals,the harm is incalculable,which makes the removal of heavy metal pollution an urgent problem.Therefore,the prevention and control of heavy metal pollution and the rational resource utilization of aluminum sludge in waterworks become the focus of this paper.In this paper,the characteristics of Al-WTR adsorption of heavy metals will be analyzed,the control of heavy metals and Al-WTR to provide a theoretical basis.Typical sludge for waterworks was collected and the main components of sludge were studied by XRF（ray fluorescence spectrometry）.The different particle size of Al-WTR、pH、initial concentration and temperature was studied to analyse the influence in those conditions.The adsorption model of Pb²⁺,Cr⁶⁺and Hg²⁺from Al-WTR were studied.The adsorption mechanism and features of the competitive adsorption of single and polysystem heavy metals were studied by static adsorption experiments.The main conclusions were summarized:（1）In the single system,pH,sludge particle size,adsorption time,initial heavy metal concentration and temperature all have important effects on the adsorption of heavy metal ions by Al-WTR.The maximum adsorption capacities of Pb²⁺,Cr⁶⁺,Hg²⁺and Cd²⁺on Al-WTR were 70.00mg/g,40.15mg/g,69.13mg/g and 24.38mg/g,respectively.With the increase of pH,the adsorption capacity of Pb²⁺and Hg²⁺increased,while that of Cr⁶⁺decreased significantly at pH>2.The decrease of particle size of Al-WTR will increase the adsorption capacity of sludge to heavy metals.The increase of adsorption capacity is due to the increase of specific surface area of sludge after particle size reduction,which can provide more adsorption contact sites.The adsorption patterns of Pb²⁺,Cr⁶⁺and Hg²⁺are roughly divided into rapid growth stage and slow equilibrium stage.The increase of initial concentration can effectively strengthen the equilibrium adsorption amount of three heavy metal ions.The increase of temperature is beneficial to the adsorption of three heavy metals by Al-WTR.（2）Pb²⁺and Hg²⁺showed strong adsorption competition in a multivariate system,When Cr⁶⁺and Hg²⁺coexist,the adsorption on Al-WTR shows a synergistic promoting effect.The adsorption sequence of four heavy metals Pb²⁺,Cr⁶⁺,Hg²⁺and Cd²⁺by Al-WTR was Pb²⁺>Hg²⁺>Cd²⁺>Cr⁶⁺under the action of various factors.Among them,the binding capacity of Pb²⁺and Hg²⁺to Al-WTR is much higher than that of Cd²⁺and Cr⁶⁺.The adsorption rates of the four heavy metals were Hg²⁺>Pb²⁺>Cd²⁺>Cr⁶⁺.Hg²⁺reached adsorption equilibrium much faster than the other three metals.（3）The adsorption kinetics of three heavy metals adsorbed by Al-WTR is well fitted by the quasi-second-order kinetic equation.The adsorption models show that the adsorption isothermal curves of Al-WTR to Pb²⁺,Cr⁶⁺and Hg²⁺conform to Langmuir model.The adsorption processes of the three models are all oriented towards entropic,endothermic and spontaneous reactions.The change of enthalpy in the whole adsorption process is relatively large,and the temperature increases,which is more conducive to the adsorption.（4）The adsorption of Pb²⁺by Al-WTR involves the results of electrostatic,ion exchange and co-precipitation interactions.Adsorption of Hg²⁺is the result of comprehensive actions,including electrostatic action,intra-particle diffusion mechanism,and reaction with oxygen-containing functional groups.The removal of Cr⁶⁺by Al-WTR is the result of adsorption–reduction.