Passivation Of Cu And Pb In Soils By Humin

Heavy metal pollution has become an urgent environmental problem to face and solve in the context of the rapid development of China’s industry.The pollution of heavy metals in soil has become one of the most serious environmental problems of global concerns.Since the accumulation of heavy metal in soil could not be found easily and not biodegradable,the heavy metal in the soil not only destroy the microbial community and population structure in soil,restrain the grown of crop,but also flow and enrich within the body of various nutrients through the food chain,and ultimately they will enter the human body,which will seriously threaten human life and health.In situ passivation technology refers to the change of heavy metals morphology and reduction of its bioavailability and migration in soil by applying some organic or inorganic chemical substances to soil,changing the physical and chemical properties of the soil,or reacting t he added chemical substances with the heavy metals in soil.Compared with other repair techniques,it has the superiority of good repair effect,short repair period,low cost and simple operation.In this paper,the Box-Behnken design methodology including five factors: adsorption time,adsorbent dosage,pH,temperature and initial concentration of Cu²⁺、Pb²⁺ was employed to study the adsorption rate of Cu²⁺、Pb²⁺from aqueous solution by humin.A quadratic model for predicting the optimum adsorption conditions was derived.Soil incubation experiments were conducted with humin and potassium dihydrogen phosphate combined application to investigate the dynamics of heavy metal fractions of simulated Cu、Pb contaminated soil.Toxic leaching extraction（TCLP）was evaluated the remediation effect of humin with potassium dihydrogen phosphate.The study showed that:Box-Behnken experiment indicated dosing quantity,pH,initial concentration of Cu²⁺,the pH and temperature in the secondary term,and the interaction between the adsorption time and dosing quantity as significant factors in the process of adsorption of Cu²⁺.And dosing quantity,pH,temperature,initial concentration of Pb²⁺,the pH in the secondary term,and the interaction between the pH and temperature were significant factors in the process of adsorption of Pb²⁺.The adsorption rate reached 80.78% at the optimized conditions of adsorption time 110 min,adsorbent dosage 2.4 g·L-1,pH= 5.4,temperature 25 ℃ and initial concentration of Cu²⁺ 208 mg·L-1.The adsorption performance was well fitted with the Langmuir isotherm model,the maximum adsorption capacity presenting 88.97 mg·g-1.The adsorption rate reached 92.59% at the optimized conditions of adsorption time 85 min,adsorbent dosage 1.2 g·L-1,pH= 4.7,temperature 44.5 ℃ and initial concentration of Pb²⁺ 202 mg·L-1.The adsorption performance was well fitted with the Langmuir isotherm model,the maximum adsorption capacity presenting 170.28 mg·g-1.The adsorption of Cu²⁺ and Pb²⁺ by humin was remarkable,which could be used as a good material for the new ion adsorbent.Physical adsorption occurred readily on the loose and porous surface of humin,and active groups such as hydroxyl,amino,carboxyl,the C = C bond and carbonyl group participated absorption by complexation with Cu²⁺、 Pb²⁺,accompanied by ion exchange of Na,Ca,Mg ions with Cu²⁺、Pb²⁺.It is revealed that humin is an green,effective and low-cost absorbent for the treatment of Cu²⁺、Pb²⁺contaminated water.During the 150 days,the pH of soil with humin only showed increasing trend;the pH of soil with potassium dihydrogen phosphate alone or combined with humin was increased with incubation time,and decreased slowly after reaching a peak.Soil pH in treatments with these amendments was all higher than that of the control.Concentrations of soil TCLP and acid extractable Cu and Pb were significantly decreased with the application of all amendments,and the oxidizable,reducible and residual Cu、Pb all have different amplitude increase.This implied that all these amendments could transform soil heavy metals from available fractions to potentially available or non-available fractions,and then remedied the heavy metals contaminated soils.The desorption rate of Cu 、 Pb in soil increased with the increasing tartaric acid concentration and the decreasing pH.Humin and defined amount of potassium dihydrogen phosphate can improve the stability of passivation.