不同湿度条件下外源铅、锌在土壤矿物中的形态转化

湿度条件是影响重金属在土中存在形态的重要因素之一,通过对纯高岭土和石英砂矿物中添加外源铅、锌离子,并在恒干、干湿交替和恒湿三种条件下培养32 d,中间按照BCR法测定了铅、锌的形态并测定了土样的p H和阳离子交换量(CEC)的变化。研究发现可溶态外源铅、锌进入惰性石英砂中有2.5%转化成可还原形态(F2),并且经过不同干湿条件下的养护后,转化到其他形态的总量不超过10%,说明重金属本身在土中的形态变化较小。进入高岭土中的可溶态铅、锌立即有34%转化成其他形态,而且随着培养时间的增加,可交换态(F1)和可氧化态(F3)含量大多降低并向F2和残渣态(F4)转化,其转化速率是恒干干湿循环恒湿。土样的p H均随培养时间先降低后增加,而高岭土的CEC总体持续降低,说明在老化过程中养护条件会促进高岭土与阳离子的结合,并且使结合的阳离子不断向矿物晶格内部转移,从而向更稳定的结合形态转化。

Speciation transformation of lead and zinc in soil minerals under different curing humidity conditions

Humidity condition is an important factor affecting the speciation of heavy metals in soil. In this paper exogenous lead and zinc ions were added simultaneously to the pure kaolin and quartz sand samples, then the polluted samples were maintained for 32 days in the conditions of constant dry, dry-wet cycle, and constant wet separately. The speciation of lead and zinc in soil samples were determined by the Community Bureau of Reference (BCR) method , and the pH and cation exchange capacity (CEC) were also measured in the process of curing. It was found that 2.5% of the soluble lead and zinc in the inert quartz sand were transformed into the reducible form(F2), and the total amount converted to other forms under different curing conditions did not exceed 10%, which indicates that the speciation change of heavy metal itself in soil is small. Soluble lead and zinc in the kaolin immediately converted into other forms with the percentage of 34, the content of exchangeable form (F1) and oxidizable form (F3) in kaolin decreased and converted to the F2 and residual form (F4) with the increasing of the curing time. The order of transformation rates is constant dry> dry-wet cycle > constant wet. The pH value of soil samples decreased firstly and then increased, and the CEC of kaolin continued to decrease, which means that the curing condition would promote the combination of kaolin and cations, and accelerate the bound cations transfer to the interior of the mineral lattice continuously, thereby convert to a more stable binding form.