Effects of exogenous salinity (NaCl) gradient on Cd release in acidified contaminated brown soil

Taking acidified Cd contaminated brown soil in Yantai as the research object, based on different exogenous salinity (NaCl) gradient (0%, 0.3%, 0.6%, 0.9%, 1.5%, 2% and 5%), indoor simulation experiments of Cd release were carried out after field investigation. Results showed that there was a significantly positive relation (r>0.90) between Cd release concentration/amount/ratio and exogenous salt (NaCl). Besides, the more exogenous salt (NaCl) was added; maximum release concentration/amount of Cd appeared the earlier. It was found that exogenous salt (NaCl) addition could obviously promote Cd release from acidified Cd contaminated brown soil. It was believed that this could be mainly due to the cation exchange between Cd²⁺ and Na⁺, together with the dissociation and/or complexation between Cl^- and Cd²⁺. In addition, available adsorption sites reduction by exchange base in soil causing Cd changed from solid state to soil solution was also a probable reason.