利用全反射X射线荧光光谱法研究土壤中活动态元素提取动力学

A study of the kinetic model of leaching mobile forms of elements in soils by the total reflection X-ray fluorescence spectrometry

活动态提取技术是深穿透地球化学研究隐伏矿的有效手段之一。提取时间是活动态提取技术的一个关键因子,由于提取剂与目标元素、赋存矿物的作用方式不同,提取时间对提取效果的影响会不同。本研究采用全反射X射线荧光光谱法(TXRF)测定土壤中Cu、Pb、Zn、Ni、Mn活动态提取量随提取时间的变化。结果表明,在1 h内,分析元素提取量随提取时间急速增长,在7 h内提取量增长速率较高,分析元素提取量基本在24 h达到平衡。对各元素的提取过程建立了两点动力学模型wt=w1exp(-k1t)+w2exp(-k2t),模拟提取土壤中两种吸附形式的活动态元素,方程中k1代表非专性吸附活动态(如离子态、静电吸附、以纳微颗粒形式存在)的提取速率常数,提取速率较快,k2代表专性吸附的活动态(粘土吸附态、铁锰氧化物弱结合或有机络合态)的提取速率常数,提取速率相对较慢。

The leaching of elements of mobile forms is one of the effective techniques in deep penetrating geochemistry in search of concealed deposits. The leaching time as an important factor has a great effect on the leaching results because of the different action modes of extractant, target elements and minerals. The total reflection X-ray fluorescence spectrometry(TXRF) was used to determine the change of the leaching amount of mobile forms of Cu, Pb, Zn, Ni and Mn with the leaching time. The results showed that the leaching amount of analytical elements increased rapidly within 1 hour, increased at a high rate within 7 hour and reached a balance at 24 h. The nonlinear kinetic model of wt = w1 exp(-k1t) + w2 exp(-k2t) was established to simulate the leaching course for mobile forms of elements adsorbed by two forms in soils. In the equation, k1 which is relatively fast represents the leaching rate of the non-obligate adsorption of mobile forms of elements such as ion form, electrostatic adsorption form, and existence in the form of nanoscale metal particles, while k2 which is relatively slow represents the leaching of the obligate adsorption of mobile forms of element, such as clay adsorption form, weak binding form of iron and manganese oxide or organically bound form.The kinetic model further provides a basis for exploring the leaching mechanism of mobile forms of elements.