Effect of Low-Molecular-Weight Organic Acids on Nano-Hydroxyapatite Adsorption of Cadmium and Lead

This study researched the effect of low-molecular-weight organic acids LMWOAs) on nano-hydroxyapatite nHAP) adsorption of cadmium as Cd2+ and lead as Pb2+. The effects of nHAP adsorption of Pb2+ and Cd2+ in the presence of 0, 0.5, 1.0, 1.5, 2.0, 3.0 and 5.0 mmol/L oxalic acid, malic acid, and citric acid were separately investigated. The contents of Pb2+ and Cd2+ in culture solutions were determined using inductively coupled plasma-mass spectrometry. The adsorption capacities of Pb2+ and Cd2+ on nHAP were calculated. The nHAP adsorption capacities varied with the different organic acids; nHAP showed the best adsorption rate under the conditions using oxalate. As the pH value of the culture solution increased, the nHAP adsorption rates were reduced. Acetic acid, malic acid, citric acid, and oxalic acid promote the fixing of lead on the nHAP surface; however, ethylene diamine tetraacetic acid EDTA) and lead form an EDTA-lead compound. Thus, EDTA inhibits nHAP adsorption of Pb2+. In contrast, LMWOAs inhibit nHAP adsorption of Cd2+, and as the Cd content in solution increases, the inhibition ability of the organic acids gradually increases. This study may provide a useful reference for the accurate evaluation of the utilization and promotion of nHAP in environmental applications