钴在黄土中的化学形态

STUDY ON CHEMICAL FORM OF Co IN LOESS

采用连续提取法 ,测定了钴在黄土中的化学形态分布。黄土样采自中辐院野外试验场 ,8个黄土样中分别加入不同量的钴溶液。钴的化学形态分为水溶态钴 (W- Co)、可交换态钴 (EXC- Co)、碳酸盐结合态钴 (CA- Co)、铁 -锰氧化物结合态钴 (Fe,Mn· OX- Co)、有机质结合态钴 (OM- Co)和残渣态钴 (RES-Co)。实验结果表明 ,在钴总含量 [Σ Co,i ]较低 [(1 0～ 40 0 )× 1 0 - 6]时 ,Fe,Mn·OX- Co占优势 ,其α值 (该形态钴含量占钴总含量的份额 )高达 5 0 %～ 80 % ;在钴总含量较高 [(40 0～ 30 0 0 )× 1 0 - 6]时 ,占优势者为CA- Co,其α值为 5 4%～ 77%。引起 CA- Co的α值从约 6 %急剧增大至 5 4%以上的钴总含量为化学形态剧变界值 ([Co]0 ) ,本试验场黄土的 [Co]0为 (40 0～ 5 0 0 )× 1 0 - 6。实验结果说明 ,当 [ΣCo,i]低于 [Co]0时 ,钴进入黄土后将优先生成 Fe,Mn· OX- Co;当 [ΣCo,i]高于 [Co]0时 ,CA- Co是钴在黄土中的主要化学形态。这将使黄土对钴有较强的阻滞能力。

The chemical form distribution of Co in loess is determined through sequential extraction. The loess sample is collected from CIRP's Field Test Site. Different Co solutions were added to eight loess samples. The chemical forms of Co can be divided into water soluble (W Co), exchangeable (EXC Co), carbonate complex (CA Co), Fe Mn Oxide complex (Fe,Mn·OX Co), organically complex ( OM Co), and residue (RES Co). The results show that the Fe Mn oxide complex (Fe,Mn·OX Co) is dominant when the total amount of Co is lower [(10～400)×10 -6 ], and its α value (fraction of Co content with certain chemical form over the total) can be high from 50% to 80%. The carbonate complex (CA Co) will be dominant when the total amount of Co is high [(400～3000)×10 -6 ], and its α value ranges from 54% to 77%. Total amount of Co causing a rapid increase of α value of CA Co from about 6% to more than 54% is called critical value of chemical form change, [Co] 0. In this experiment, [Co] 0 of loess is [(400～500)×10 -6 ]. The results show that when the total amount is lower than [Co] 0, Co will exists mainly in the state of (Fe,Mn·OX Co) when it meets with loess; while the total amount is higher than [Co] 0, CA Co will be the dominant state, so loess will have strong retardation to Co. (