Immobilization of cadmium (Cd2+) in contaminated soil using biochar derived from Calophyllum inophyllum (bitaog) seed husks

Abstract

Many heavy metals such as cadmium found in contaminated soil naturally leach out and seep in groundwater through time. Natural leaching is further accelerated in acidic conditions specifically with acid rain. This study investigated the effectiveness of biochar derived from Calophyllum inophyllum (Bitaog) seed husks as an immobilizing agent through a simulated acid rain leaching test (equivalent to 100 years of acid rain) using artificially contaminated soil. Furthermore, magnetization and phosphoric acid treatment were utilized to produce modified biochar where Thermo-gravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), and Fourier Transform Infrared Spectroscopy (FTIR) analyses revealed that the modifications led to the enhancement of physiochemical properties such as fixed carbon content, surface morphology, and surface chemistry respectively. Walkley-Black Loss on Ignition test showed that all the biochar amendment increased the organic matter content of soil making it attractive for in-soil applications. Adsorption kinetic and isotherm models were used to describe the adsorption mechanism of cadmium onto the soil amended with modified and unmodified biochar where experimental results showed that the adsorption best fitted the pseudo-second order kinetic and Langmuir isotherm models. The leaching test results showed that the soil amended with magnetic and phosphoric acid modified biochar were not suitable as immobilizing agents especially in highly acidic conditions. Whereas the unmodified biochar significantly reduced leached cadmium concentration by 40.02% than in unamended soil as shown by the AAS results. Bitaog derived biochar was affirmed to be potentially effective for the long-term immobilization of cadmium in contaminated soil while may simultaneously increase soil fertility.