摘要
【目的】研究雷州半岛水稻土吸附Cr(Ⅵ)反应特征以及零价铁粉对水稻土中Cr(VI)的还原作用,分析相关因素对上述过程的影响。【方法】通过批处理等温吸附和动力学实验,考察反应物浓度、时间、pH、离子强度和陪伴离子等因素对Cr(Ⅵ)吸附量和还原比例的影响,并用相关反应模型对数据进行拟合分析。【结果】在所研究的0.1～2.0 mmol/L初始浓度范围内,水稻土对Cr(Ⅵ)吸附未达到饱和,吸附等温线可用Langmuir方程拟合(R2=0.9963)。提高pH和离子强度将抑制C(Ⅵ)吸附,且吸附动力学曲线可用假一级反应动力学方程拟合(R2=0.9935)。在所研究的反应条件下(初始溶液pH_4.0、0.20 mmol/L Cr(Ⅵ)、0.01 mmol/L NaCl、5.0 g土+0.25 g零价铁粉、体系总体积250 mL),Cr(Ⅵ)还原比例可达100%。溶液中Cr质量衡算表明,所生成的Cr(Ⅲ)可部分被吸附到固体表面。磷酸根和邻菲罗啉的存在均可降低Cr(Ⅵ)还原比例,提高反应体系pH不利于Cr(VI)还原,其比例可从pH_4.34时的100%下降至pH6.87时的56.3%。【结论】水稻土吸附Cr(Ⅵ)反应机理包含静电吸附,高pH条件所导致的土壤表面对Cr(VI)的静电斥力增加以及背景电解质中阴离子的竞争吸附均可减少水稻土对Cr(Ⅵ)的吸附量;零价铁粉对水稻土中Cr(Ⅵ)的还原比例随pH升高逐渐减少,且磷酸根的存在有抑制作用。
【Objective】The present study aimed to reveal the reaction characteristics of Cr(Ⅵ) adsorbed by paddy soil and examine the reduction effect of Cr(Ⅵ) by zero-valent iron ( ZVI,) in the soil, and analyze the effect of relative factors on the above-mentioned process.【Method】The batch isotherm adsorption and kinetics experiments were performed to investigate the effects of reactant concentration, reacting time, pH, ionic strength and accompanying anions on the adsorption and reduction of Cr(Ⅵ) in the mixed system of paddy soil and ZVI. The experimental data was also analyzed with adsorption and kinetic model.【Result】The adsorption saturation was not obtained with the initial concentrations ranging from 0.1 to 2.0 mmol/L and the adsorption isotherm could be well fitted by Langmuir equation (R2=0.9963). The increase in pH and ionic strength was unfavourable for Cr(Ⅵ) adsorption and the kinetic curve could be properly fitted by pseudo-first-order kinetic equation (R2=0.9935). With the introduction of ZVI, the added Cr(Ⅵ)(0.20 mmol/L ) was totally transformed to Cr(Ⅲ) under the present reaction condition, and the calculation of aqueous Cr mass balance indicated that a certain amount of the generated Cr(Ⅲ) were adsorbed by the solid surface. The presence of phosphate and 1,10-phenanthroline could inhibit the Cr(Ⅵ) reduction. Moreover, Cr(VI) reduction would be suppressed as the solution pH increased, evidenced by the reduction percentage decreased from 100% at pH 4.34 to 56.3% at pH 6.87.【Conclusion】The electrostatic adsorption was involved in Cr(Ⅵ) adsorption by the paddy soil. The enhancement of electrostatic repulsion between the soil surface and Cr(Ⅵ) and the competitive adsorption between Cr(Ⅵ) and chloride ions contained in the supporting electrolyte could jointly decrease the Cr(Ⅵ) adsorption in the soil. Low pH was favourable for the occurrence of Cr(Ⅵ) reduction by ZVI in the soil, and the reduction would be inhibited in the presence of phosphate and 1,10-phenanthroline.
作者
张亚莉
杨杰文
ZHANG Yali;YANG Jiewen(College of Agriculture,Guangdong Ocean University,Zhanjiang 524088,China)
出处
《广东农业科学》
CAS
2019年第4期51-57,共7页
Guangdong Agricultural Sciences
基金
国家自然科学基金面上项目(41671235)
