多核复合无机高分子混凝剂的制备及混凝机理

Coagulation mechanism of the multi-core poly-silicate composite coagulant and its preparation

用石墨化学纯化产生的酸性和碱性废水,以直接中和法制备不同pH值的聚硅酸多核复合型无机高分子混凝剂。在50℃下,对制备的混凝剂进行常压干燥,得到固体产品后进行结构表征。FT-IR结果表明,适宜pH值下有Si—O—Al和Si—O—Fe生成;XRD图谱也表明,多核复合混凝剂含有新的化学物质而非原材料的简单混合。不同pH值混凝剂的微观结构稍有不同。混凝试验表明,混凝效果与混凝剂微观结构有关,适宜pH值(2.77、3.60)的复合混凝剂可以得到好于常规硫酸铝的混凝效果。在最优剂量下,PAFSS(多核复合混凝剂主要成分为Si、Al、Fe及SO24-,pH=3.60)对垃圾渗滤液中COD和重金属Cr的去除率分别达55%和97%;pH值太高时(3.98),混凝剂不稳定,混凝效果变差。研究表明,多核复合混凝剂中所含的少量具有混凝作用的Mg2+、Ti4+、Zn2+等对混凝效果具有协同作用。

The present paper is to introduce our study of coagulation mechanism of the multi-core poly-silicate composite coagulant and its preparation. Multi-core poly-silicate composite inorganic polymer co- agulants .with different pH values have traditionally been prepared by the acidic and alkaline sewage left-over in the chemical purification of graphite. More specifically speaking, SiO2, Fe2O3, Al2O3 serve as the main impurities of graphite ores whereas MgO, TiO2, ZnO are the less popular ones. The impurities from graphite ores are usually ex- tracted by alkali roasting when the process of extraction was tradition- ally conducted at high temperatures ranging from 500 ℃ to 900 ℃. The whole process of extraction usually includes alkali roasting, wa-ter-cleansing, acid leaching and, last of all, drying. In this process, SiO2 and extra alkali were washed into alkaline sewage, with the met- al oxides, such as Fe2O3, Al2O3 and extra acid turned into acidic sewage. However, in this paper we have done our simulated experi- ment in the real laboratory conditions with acid and alkaline sewage generated. We have managed to obtain the multi-core poly-silicate composite inorganic polymer coagulant product by neutralization reac- tion of acid and alkaline sewage under pH value control. And, later, we have succeeded in drying the liquid coagulants at 50℃ under the atmospheric pressure, whose micrestructure has been characterized by Fourier transform infrared spectroscopy （FT- IR） and X-ray diffrac- tion （XRD）. The results of FT - IR indicate that at appropriate pH value, it is possible to observe the peaks corresponding to Si--O--Al and Si--O--Fe vibration. The XRD spectra can display that the composite coagulant reveals a new chemical matter rather than a mere mixture of raw material. When the coagulation behaviors were evalu- ated through a jar test by treating landfill leachate, at optimal dosages, the removal efficiency of Cr and COD can reach 97 % and 55%, respectively, if treated by PAFSS （3.60）. In addition, the coagulation experiments demonstrate that there exists a corresponding relationship between the coagulation effect and the microscopic struc- ture. The composite coagulant with appropriate pH value （2.77, 3.60） had a better coagulation effect than the conventional aluminum sulfate, whose coagulation effect may get deteriorated if pH value turns too high （3.98）. In addition, the synergistic effect of small amounts of Mg2＋ , Ti4＋ , Zn2 ＋ also proves to be an important factor in the composite coagulant behaviors.