不同pH下低分子量有机酸对黄壤中铝活化的影响

EFFECT OF LOW-MOLECULAR-WEIGHT ORGANIC ACIDS ON THE MOBILIZATION OF ALUMINUM IN YELLOW SOIL

用一次平衡的方法研究了不同pH下低分子量有机酸对黄壤中铝活化的影响.结果表明,低分子量有机酸体系可以通过质子和有机酸阴离子两个因素促进黄壤中铝的活化.当pH>4.3时,有机酸通过络合作用促进铝溶解的大小顺序为:柠檬酸>草酸>水杨酸>乳酸,与有机酸和铝形成络合物的稳定常数大小一致.有机酸阴离子可以通过自身的吸附增加土壤交换态铝的量,但质子作用对黄壤交换态铝的活化比有机酸阴离子的吸附起着更为重要的作用,随pH值的降低这种趋势更加明显.有机酸对交换态铝的活化作用随pH值的降低而增加.低分子量有机酸活化的铝主要分布在土壤表面的交换位上,但在柠檬酸和草酸体系中,当pH值分别大于4.40和4.55时,活化铝主要分布在土壤溶液中.

Soluble and exchangeable Al were the most active species in soil. The effect of low-molecular-weight (LMW) organic acids on the mobilization of aluminum in yellow soil was investigated with a batch test. The results showed that LMW organic acids were able to promote the mobilization of aluminum through proton and organic anions. When pH is more than 4.3, the ability of organic acids to promote the aluminum dissolution by complexation follows the order as citrate > oxalate > salicylate > lactate, which is consistent with their (stability) constants of aluminum-organic complexes. The presence of organic acids induced an increase in soil exchangeable Al through the adsorption of organic anions by soil, while the proton showed the larger effect on the mobilization of exchangeable Al than that of organic anion adsorption at low pH. The effect of organic acids on exchangeable Al increased with decreased pH. The aluminum mobilized by organic acids mainly existed as exchangeable Al on soil exchangeable sites, however, in citrate and oxalate systems, when pH was more than 4.40 and 4.55, respectively, most of mobilized aluminum existed as soluble Al in solution.