净水厂污泥对水中Cr^(3+)的吸附去除研究

Adsorption removal of trivalent chromium from sewage by drinking water treatment sludge

净水污泥是净水厂生产过程中产生的废弃副产物。选取北方地区某净水厂的净水污泥,利用批量试验研究了不同pH值污泥对Cr3+的吸附效果、不同初始质量浓度污泥对Cr3+的吸附动力学和不同温度条件下污泥对Cr3+的吸附热力学以及吸附解吸。结果表明,净水污泥由铝氧化物、铁氧化物和有机物质构成,表面多孔并且为无定型非晶体结构。在酸性条件下,净水污泥对Cr3+的吸附性能随pH值增加而增大,不同pH值条件下Cr3+的形态分布对吸附性能有一定影响。吸附过程符合拟二级反应动力学模型,决定系数达到0.999以上,说明吸附过程以化学吸附为主;污泥对Cr3+的吸附符合Freundlich方程,KF值随温度增加而增大,说明温度升高能够增加吸附剂的吸附能力。热力学参数ΔG<0、ΔH>0、ΔS>0,说明吸附过程是自发进行的,吸附属于吸热反应并且反应后系统的无序性增加。在0.1 mol/L和0.5 mol/LHNO3溶液作为解吸剂的条件下,Cr3+可以有效地解吸出来,相对解吸率分别达到72.33%和82.96%,解吸后的污泥残渣中铬离子质量比符合国家城镇污水处理厂污泥处理标准,可以将污泥残渣运送至污水处理厂统一处理。研究表明,净水污泥作为一种新型吸附材料,可以安全有效地应用到重金属废水处理中。

In this paper, we would like to explore the potential for the recycled use of sludge to recover heavy metal contents as an ad sorption material for industry. As is known, the leftover sludge from drinking water treatment is rich in heavy metal contents as an un avoidable byproduct of drinking water purification process. For the purpose of recycled use of the heavy metal remnants, we have chosen sludge samples from a water treatment plant in a Chinanorth cold re gion and laid out a systematic method for batch tests for investigating the adsorptive efficiency of the sludge for Cr3 ＋ at different pH values, while using the adsorption kinetics at different initial concentrations of Cr3＋ , and the adsorption thermodynamics at different temperatures. At the same time, we have also conducted a series of desorption tests. The results of our experimental tests have demonstrated that there is a great potentiality to use the drinking water treatment sludge to recover the precious reusable chemical metal and nonmetal con tents of aluminum （hydr） oxides, iron （hydr） oxides and some other organic substances. The sludge samples we had chosen enjoy a porous structure on the surface and possess various amorphous forms. Under acidic conditions, the adsorption tends to behave more actively with the increase of the pH value, at the same time, the species of Cr3 ＋ distribution at various pH values tend to display their effects on the overall behaviors of the different chemicals. The data of adsorption kinetics under our observation tend to reveal that the adsorption po cess should fit the pseudo secondorder reaction kinetics, and the correlation coefficients were likely to reach all above 0. 999, suggesting that the adsorption process seems to be dominated by the chemical adsorption process. It seems to us that the data of adsorptive isotherms best fit the Freundlich model for the reaction process, in which the Kv contents tend to increase with the increase of the tem perature, implying that its increase is likely to be able to strengthen the adsorptive capacity of the adsorbents. The results of thermody namic evaluations, in which xG 〈 0, AH 〉 0, AS 〉 0, tend to prove that the adsorption process turned out to be a spontaneous, en dothermic process and randomness increased through the adsorptive process. When added concentrations of the desorption agent, it has been found that HNO3 would be 0.1 mol/L and 0.5 moL/L. As a re suit, Cr3 tended to get dissolved efficiently from the sludge, with their desorption rates being 72.33 % and 82.96 %, respectively. The contents of Cr3 ＋ in the sludge residuals prove to be in accord with the national standard for the urban sewage processing plant sludge, thus showing that it is possible for the sludge from the drinking water treat ment to be applied safely and efficiently in a heavy metal sewage treatment process as a novel adsorbent with a great potentiality of re cycled application.