载镁生物炭对水体中磷酸盐和植酸的吸附性能及机理分析

水体中磷的大量存在引发了水体富营养化,导致水质逐步恶化、黑臭。为了有效处理水体中的磷(主要有磷酸盐和植酸类),采用成熟竹子为原料、氯化镁为改性剂,以氮气热解法制备载镁生物炭,对水体中磷进行吸附研究,同时实现对生物炭的资源化利用。通过载镁生物炭对无机、有机磷在水体中的动力学实验和解析实验,并结合X射线衍射、扫描电镜、傅里叶变换红外光谱等技术研究了载镁活性炭对磷酸盐及植酸的吸附性能及机理。结果表明:载镁生物炭对两种类型磷的吸附量较单一生物炭均显著提高,对磷酸盐和植酸的吸附平衡量分别达到105,165 mg/g。载镁生物炭对2种磷的吸附动力学均符合准二级动力学拟合方程,吸附等温线符合Langmuir和Freundlich方程,其对有机磷植酸的最大吸附量高于磷酸盐,吸附过程受多种机理共同作用,以化学沉淀吸附为主。此外,吸附过程中载镁生物炭分别与磷酸盐、植酸生成了针状的磷酸镁水合物和非晶态的含镁磷的复合物。

ADSORPTION PERFORMANCE AND MECHANISM OF PHOSPHATE AND PHYTIC ACID ON MAGNESIUM-LADEN BIOCHAR IN WATER

The large amount of phosphorus in the water led to eutrophication, deterioration of water quality and thus made black and odorous water. In order to treat phosphorus mainly including phosphate and phytic acid in water, Mg-laden biochar was prepared with bamboo and magnesium chloride by nitrogen pyrolysis to adsorb inorganic phosphorus and organic phosphorus in water, and at the same time, realized resource utilization of biochar. In this paper, the kinetics and adsorption equilibrium as well as desorption of phosphate and phytic acid adsorbed on Mg-laden biochar in water were studied. The adsorption mechanism of phosphate and phytic acid on Mg-laden biochar was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results showed that the adsorption of phosphate and phytic acid on Mg-laden biochar was significantly increased, compared to biochar; and the adsorption equilibrium concentrations of phosphate and phytic acid were 105, 165 mg/g, respectively. Both phosphate and phytic acid kinetic results complied well with the pseudo-second-order. Both Langmuir and Freundlich model produced the adsorption isotherm data well. The maximum adsorption of phytic acid was much higher than that of phosphate and the adsorption process was controlled by multiple mechanisms, dominated by chemical precipitation adsorption. Characterization results from XRD, SEM and FTIR showed that Mg-laden biochar formed needle-like magnesium phosphate hydrate with phosphate, and amorphous magnesium-phosphorus complex with phytic acid.