Effect of Paper Mill Sludge on Adsorption and Desorption of Cd(II) and Pb(II) in Paddy Soils

There are high organic matter and cation exchange capacity (CEC) in paper mill sludge, which can be used efficiently to amend soil properties and promote the growth of crops. The batch method was used to investigate effects of paper sludge on adsorption and desorption of Cd (II) and Pb (II) in two types paddy soil (red soil, purple soil), through adding paper sludge to red soil and purple soil. The results showed that isothermal sorption process of Cd (II) and Pb (II) by soils and paper sludge could be well described by Langmuir equation and Freundlich equation, and all coefficients (r) were higher than 0.9. The purple soil had a higher sorption capacity of Cd (II) and Pb (II) than red soil. The sorption capacities of Cd (II) and Pb (II) in soils increased after added paper sludge, and they reached adsorption equilibrium as the percentages of paper sludge were 10%, 1% in red soil and purple soil, respectively. The desorption capacities of Cd (II) and Pb (II) in soils decreased after added paper sludge, and they reached minimum as the percentages of paper sludge were 5%, 2% in red soil and purple soil, respectively. It was better to immobilize Cd (II) and Pb (II) after added paper sludge, thus paper mill sludge can relieve the migration of heavy metals in soil-crop systems. It can provide a new way for safe using of heavy metal contaminated soil and resource utilization of paper sludge.