Calcium alginate-nZVI-biochar for removal of Pb/Zn/Cd in water: Insights into governing mechanisms and performance

Heavy metals pollution in water caused by the intensification of industrial processes and human activities has attracted worldwide attention. Finding an environmental-friendly and efficient remediation method is in need. In this study, the calcium alginate entrapment and liquid-phase reduction method were used to prepare calcium alginate-nZVI-biochar composite (CANRC), which was firstly used to remove Pb2+, Zn2+, and Cd2+ in water. The effects of pyrolysis temperature, solution pH, and coexisting ions, etc. during adsorption processes were explored. Scanning electron microscope-Energy dispersive spectrometer (SEM-EDS), X-ray diffraction spectroscopy (XRD), and X-ray photoelectron spectroscopy (XPS) were used to characterize the physicochemical properties of CANRC before and after adsorption. Different adsorption models and site energy analysis were used to analyze the possible mechanisms. The results showed that CANRC prepared at 300 & DEG;C and a 5 wt% Fe loading ratio had the maximum adsorption capacities with a dosage of 2.5 g/L and pH = 5.0- 6.0. The adsorption process was more in line with the Langmuir isotherm model dominated by monolayer adsorption. The maximum adsorption capacities of Pb2+, Zn2+, and Cd2+ were 247.99, 71.77, and 47.27 mg/g, respectively. Site energy analysis combined with XRD and XPS analysis indicated that surface complexation and precipitation were the main adsorption mechanisms. This study provides an alternative way for the removal of heavy metals from water.

Automated summary

Heavy metals pollution in water caused by industrial processes and human activities has become a global concern, highlighting the need for an environmentally friendly and efficient remediation method. In this study, a calcium alginate-nZVI-biochar composite (CANRC) was prepared using calcium alginate entrapment and liquid-phase reduction method to remove Pb2+, Zn2+, and Cd2+ from water. The effects of various factors on the adsorption process were investigated, and the physicochemical properties of CANRC before and after adsorption were characterized using SEM-EDS, XRD, and XPS. Different adsorption models and site energy analysis were used to understand the mechanisms involved. The results showed that CANRC prepared at 300°C and a 5 wt% Fe loading ratio exhibited the highest adsorption capacities for Pb2+, Zn2+, and Cd2+, with surface complexation and precipitation identified as the main adsorption mechanisms. This study provides an alternative approach for the removal of heavy metals from water.