Adsorption Capacity Of Coal Gangue To Phosphate In Water

Eutrophication is a problem which is urgent to be solved in china and the whole world. Phosphate is the decisive factor that cause eutrophication of water bodies. Therefor, the removal of phosphate is the key to solve the problem in water bodies. Coal gangue is one of large industrial solid wastes in our country, it does harm to the ecological environment and human health when dumped in the environment. In this paper, coal gangue was used as solid adsorbent to remove the phosphate in water, providing reference data to solve the problem of eutrophication and coal gangue.A variety of analysis methods were used to analyze the character of the adsorption material, revealing the possibility of its adsorption of phosphate. The effects of different particle sizes, the pH of solution, coexisting ions, different conditions of temperature and concentration were studied. Fitting the experimental data by different adsorption isotherm models, adsorption kinetics and thermodynamic formulas to analyze the adsorption process. At the same time, the desorption ability of phosphate and the leaching of heavy metals elements in coal gangue was studied, providing a certain reference value in practical application. The main conclusions are as follows:(1) Kaolinite and quartz were the main composition of coal gangue, the structure of the coal gangue was flaky; BET test results showed that the distribution of pore diameter of coal gangue was uneven, the pore structure mainly consisted of mesoporous, a small amount of microporous and macroporous;(2) Particle size of coal gangue which was less than 200 mesh reflected good phosphate absorption performance; the optimal value of pH was 6 to 7; environmental media had little effect on the adsorption of phosphate; Higher temperature was favorable for the adsorption reaction and the adsorption process belonged to the endothermic reaction;(3) By the adsorption isotherm, it could know that the maximum adsorption capacity was 2.26 mg/g, which is higher than that of kaolinite and montmorillonite, and other natural mineral adsorption capacity of phosphate. It was found that the absorption process fitted the Langmuir model and pseudo-second-order kinetics equation, which indicated that the adsorption type were monolayer and chemical adsorption. The three stages of the intra-particle diffusion equation fitted well, indicating the reaction rate was determined by external diffusion and intra-particle diffusion. Adsorption thermodynamics showed the adsorption process was spontaneous, endothermic and physical adsorption. Combining dynamics and thermodynamics research results together, there were physical adsorption and chemical adsorption coexistence in the adsorption process of coal gangue to phosphate;(4) The desorption rate was the best in acid phosphate solution, alkaline solution followed, also there was a small amount of precipitation in the pure water. The desorption rate incresed with the increase of the concentration of acid and alkali within a certain range. After a long time of soaking, one of the heavy metal elements Zn was only checked in leaching solution of coal gangue, and the content of it is much lower than the III class standard in the 《The Environmental Quality Standards》 (GB3838-2002), which showed that coal gangue can be used as adsorbent to the adsorption and removing of phosphate in water.