稀土矿区污染农田土壤治理后稀土元素的赋存形态分析

针对赣南稀土矿区受污染农田土壤,研究添加改良剂沸石治理后土壤中稀土元素的含量及形态分布特征。分别采用酸法消解和Tessier连续提取法对土壤样品(土样)中稀土元素总量及赋存形态进行提取分析,并利用电感耦和等离子质谱仪(ICP-MS)测定其中15种稀土元素含量及其形态含量。结果表明,土样中各稀土元素总量高达1 296 mg/kg,远远高于全国土壤平均总量176.8 mg/kg,稀土钇(Y)含量高达386.01 mg/kg远高于其余14种稀土元素含量,土样中轻稀土元素含量与重稀土元素含量比值为0.66远小于全国土壤中轻稀土含量与重稀土含量比值(3.78),表明该稀土矿属重稀土富钇矿型,且加入沸石不能影响土样中稀土元素的总量变化;矿区农田土壤加入沸石治理前,碳酸盐结合态、有机物结合态、铁-锰氧化物结合态、可交换态和残渣态稀土元素含量分别占总量百分比分别为51.03%、29.6%、10.39%、7.52%和1.46%,加入沸石治理后,以上5种形态的稀土元素含量占总量百分比分别为8.19%、71.54%、9.35%、4.34%和6.58%,表明沸石对矿区农田土壤中稀土元素的形态分布有很大影响,并显著钝化稀土元素在土壤中的生物活性及可迁移性。

Speciation Analysis of Rare Earth Elements(REEs) in Farmland of Mining Area

Soil of farmland in a rare earth mining area was widely contaminated due to the in-situ leaching process.Studies were carried out to tackle the problem with the experiment investigating speciation of rare earth elements(REEs) before and after treatment by adding zeolite to the soil for pollution mitigation.Acid digestion and Tessier sequential extraction procedure were used in evaluation of the soil samples,during which contents of 15 REEs and fractions had been determined using ICP-MS.The results showed that content of REEs in the soil samples were as high as 1 296 mg/kg,well above the average of 176.8 mg/kg in the country,and an ion-adsorption type ore enriched in heavy REEs and Y was found in the rare earth mining region so addition of zeolite could not change the total content of REEs.Large amount of REEs in the contaminated farmland soil before zeolite addition featured the forms of carbonate-bonded,organic matters-bonded and iron-manganese oxides,as well as of forms of the exchangeable and residue in different proportions,and after addition of zeolite the proportion of the above five forms changed a lot,indicating zeolite significantly affect the speciation of REEs in the contaminated farmland soil,thus resulting in the passivity of activity and mobility of REEs.