Adsorption Properties and Mechanism of Modified Magnetite for Cadmium Removal from Mined Soil
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摘要:
采用酸浸、灼烧的方法对磁铁矿进行改性，通过扫描电镜（SEM）、X射线衍射（XRD）对改性前后的磁铁矿进行表征，并研究其对矿区土壤中水溶性Cd2+的吸附性能及机理。吸附条件试验表明：对于20 g矿区土壤样品，当改性磁铁矿用量0.5 g、pH为7、吸附时间70 min时，以5 mL 0.5%盐酸-0.5%硫脲为洗脱剂，改性磁铁矿对水溶性镉的去除率达到95%以上。Cd2+的吸附等温线符合Langmuir和Freundlich等温线吸附模型，饱和吸附容量达到18.93 mg/g。吸附过程不受离子强度影响，吸附机理主要为离子交换和氧化还原反应。改性磁铁矿制备简便且易分离，是一种值得进一步研究并实际应用的环保处理材料。
Abstract:Magnetite was modified with the methods of acid leaching and calcination.The surface structure of magnetite before and after modification were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD).Adsorption property and mechanism of modified magnetite on water soluble Cd2+ were investigated. The results show that:for 20 g soil samples, when the magnetite dosage is 0.5 g, pH value is 7, adsorption time is 70 min, and 5 mL 0.5% HCl -0.5% thiourea are as eluent, the maximum removal rate of water soluble cadmium can up to 95%. The Cd2+ adsorption is well fitted by Langmuir and Freundlich models and the maximum absorption capacity is 18.93 mg/g. Furthermore, the adsorption is not suppressed by the presence of background electrolyte that exists mainly ion-exchange and oxidation-reduction process. The preparation of modified magnetite is simple and easy to separate, which deserves further study and pracitical application for environmental treatment.
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Key words:
- magnetite /
- mined soil /
- cadmium /
- adsorption /
- mechanism
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表 1 正交试验结果
Table 1. The results of the orthogonal test
No. 盐酸/% 硫脲/% 体积/mL 镉回收率/% 1 1(0.25) 1(0.25) 1(5) 82.75 2 1(0.25) 2(0.5) 2(10) 94.03 3 1(0.25) 3(0.75) 3(15) 95.38 4 2(0.75) 1(0.25) 2(10) 93.61 5 2(0.75) 2(0.5) 3(15) 95.50 6 2(0.75) 3(0.75) 1(5) 86.74 7 3(0.5) 1(0.25) 3(15) 92.58 8 3(0.5) 2(0.5) 1(5) 96.83 9 3(0.5) 3(0.75) 2(10) 96.86 
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表 2 磁铁矿吸附等温线拟合参数
Table 2. Parameters of the fitting of adsorption isotherms on magnetite
Langmuir Freundlich qmax/(mg·g-1) K R2 Kf n R2 磁铁矿 12.05 0.021 0.991 0.33 2.106 0.992 改性磁铁矿 18.93 0.032 0.993 0.25 2.251 0.994 注：K和Kf分别为Langmuir和Freundlich吸附等温方程的吸附常数；n为与反应键能有关的经验常数；qmax为饱和吸附容量。
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表 3 不同矿物材料对镉的吸附容量比较
Table 3. Comparison of the adsorption capacity of cadmium with various mineral
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