臭氧化含苯酚污水投加水镁石沉淀出草酸镁的实验研究

本文通过两组不同水镁石-苯酚投料比的实验,研究固体沉淀物与水质变化的关系。实验显示,水镁石解离出的Mg²⁺与苯酚降解的中间产物能形成难溶盐,并发生沉淀分离,促进含苯酚废水臭氧化降解的效率。当苯酚的初始浓度为47 g/L,初始碳镁原子比(C/Mg)为30时,经3小时充分臭氧化曝气后,投加的水镁石全部耗尽。XRD、TG/DSC结果显示新形成的沉淀物为草酸镁。反应终点的pH值在4以下,TOC去除率为40%。当体系的初始C/Mg(原子比)为1,苯酚的初始浓度为1.5 g/L时,同样的臭氧化曝气过程体系残留的沉淀物仍是水镁石。反应终点的pH值在10左右,TOC去除率为92.8%。研究证明,苯酚臭氧化过程也是体系酸化的过程,至少在高C/Mg比条件下新生的质子能与水镁石解离出的羟基中和,水镁石解离出的Mg²⁺可与草酸根结合沉淀出草酸镁。

Experiment studies of glushinskite sediments from ozonation of phenolic wastwater in the presence of brucite

Phenolic wastewater is one of the common industrial pollution sources. Ozonation with brucite and natural hydroxide magnesium has more effective impact than single ozonation of phenol degradation. The function of brucite in ozonation of phenolic wastewater was discussed previously as OH^- from hydrolyzed Mg(OH)₂ forming basic catalyst and raising the activities of O₃. In this study, two batch experiments with different brucite-phenol ratios were carried out with close attention paid to the final sedimentary products. The experiments show that Mg²⁺ from hydrolyzed Mg(OH)₂ could combine with intermediate products of phenol oxidation to form indissoluble deposits and raise the processes of phenol degradation. When the initial concentration of phenol was 47 g/L, and the controlled dosage of brucite by C/Mg (atoms ratio of carbon to magnesium) equal to 30, the only residual solid after 3 hours O₃ aeration was glushinskite (magnesium oxalate dihydrate) which substituted for the brucite, as supported by XRD and TG/DSC examination. At the terminal of the reaction, the test solution showed pH below 4 and removal of nearly 40% of TOC (Total Organic Carbon). In a comparative experiment changing the initial concentration of phenol to 1.5 g/L with C/Mg (atoms ratio) equal to 1 and under the same condition of O₃ aeration, the residual solid of the exam was still brucite, the terminal pH was 10 and 92.8% of TOC was removed. The results from two examinations reveal that the process of ozonation of phenolic wastwater is characterized by continued acidification. At least under the higher initial C/Mg ratio condition, the primary proton can neutralize hydroxyl from hydrolyzed brucite. In this case the terminal sediments are only glushinskite. Obviously, Mg²⁺ is derived from hydrolyzed of brucite; however, glushinskite is stable in an acidic environment. Both Mg²⁺ and OH^- from brucite play a role of degrading phenol in water.