不溶性腐殖酸对重金属离子的吸附研究

Study on adsorption of heavy metal ions onto insolublized humic acid

讨论了不溶性腐殖酸(IHA)对水中重金属Pb、Cd、Cu的吸附去除作用。将可溶性腐殖酸进行改性处理,制备了不溶性腐殖酸,并应用差热分析(TGDTA)、扫描电镜(SEM)等测试手段对其热性能及微观形貌进行了分析表征。研究了不溶性腐殖酸对水溶液中的Pb、Cd、Cu等重金属离子的吸附特征。吸附等温线分别以Linear,Frendlich和Langmuir方程进行拟合,结果显示吸附的最佳模型为Frendlich方程。利用该方程拟合的数据,由ClausiusClaperyon’s方程计算出的Pb2+、Cd2+、Cu2+吸附焓变值说明,重金属在不溶性腐殖酸上的吸附以物理吸附为主。同时考察了温度、酸度及吸附时间对吸附的影响。结果表明,随着温度的升高和pH值的增大,不溶性腐殖酸对Pb2+、Cd2+、Cu2+的吸附量增加。随着pH的增加,在近中性条件下不溶性腐殖酸对重金属离子的吸附率高且稳定。当pH=7时,在实验浓度范围内Pb2+、Cd2+、Cu2+在不溶性腐殖酸中的吸附率分别为98.73%,97.86%,99.25%。吸附进行12h以后,吸附作用基本达到平衡。不溶性腐殖酸对重金属离子具有强烈的吸附作用且吸附率稳定,可以广泛用于去除污水中的重金属离子。

The present paper has investigated the removal of heavy metals Pb^2 ＋ , Cd^2 ＋ and Cu^2 ＋ from the aqueous solutions by adsorption onto insoluble humic acid （IHA） at different pH and temperatures. As is known, insoluble humic acid （IHA） has an excellent adsorptive ability, which can be prepared by heating the highly soluble HA at 330 ℃ and the treated with 2 mol/L CaCl2 solution. The insoluble humic acid are characterized by such means as thermo-gravimetry and differential thermal analysis （TG-DTA） as well as scanning electron micrograph （SEM）. While investigating the effect of temperature, pH and time on the adsorption behaviors of heavy metals, it has found that the adsorption capacity increases with the increase of the temperature and pH. At the same time, the paper has also analyzed the adsorption experimental data by using three different isotherm models： Langmuir, Frendlieh and Linear isotherm. As the result, it has obtained the optimal correlation for Frendiich isotherm equations. In addition, the paper has calculated the thermodynamic quantities AH in accordance with the Clausius-Claperyon, s theory. The △H values for Pb^2 ＋ , Cd^2 ＋ and Cu^2＋ prove to be - 75.37 J/mol, - 117.92 J/mol and - 110.76 J/mol, respectively, which are smaller than the lower limit of the chenmisorption （42.0 kJ/mol ）. It means that the type of adsorption of Pb^2 ＋ , Cd^2 ＋ and Cu^2＋ onto IHA is physisorption, rather than by chemical bonding. And finally, the adsorption equilibrium gained within 12 hours, and a high and stable removal of heavy metals on insoluble humic acid has been obtained almost under the neutral conditions. The above results suggests that IHA is a potentially efficient absorbent to purify water from the heavy metal contaminants.