Designer biochar with specific functionalities for the sustainable mining of invaluable metals from sea water: Performance assessment, mechanism insights and cost benefit analysis

Abstract

Resource efficiency and cleaner production are an integral component of sustainable development. The present research addresses three contemporary issues. Firstly, quest for a greener alterative to land based mining-seawater, secondly, translation of renewable biowastes into carbon negative biochar and thirdly, synthesis of organic salts of metals directly from metal laded biochar. Sea water is an untapped source of invaluable elements leading to rising momentum for various new technologies. Herein, neem cake is tailored specifically for selective recovery of magnesium and strontium ions from simulated sea water in both batch and continuous systems. Magnesium selective biochar is prepared by insitu pyrolysis at 700℃ using sodium bicarbonate and urea as green porogen and nitrogen source whereas strontium selective biochar is prepared by direct pyrolysis at 700℃ followed by encapsulating alginate microspheres within the biochar lattice. Batch studies revealed the maximum adsorption capacities and removal efficiencies of 34.08 mg/g and 95 % for strontium(S-BC) and 40.2 mg/g and 98 % for magnesium(M−BC). The analytics reveals biochars as fine-tuned mesoporous carbon dominant structure with several N and O functionalities suggesting complexation, H-bonding as the adsorption mechanism. The Sips and PNO models surpassed all isotherm and kinetic models and well describes the process kinetics as chemisorption along with film diffusion as main contributors respectively. In column studies, effect of different process parameters is investigated and it is observed that experimental data corelates well with the BDST model. Moreover, scale up approach is employed to predict large scale design parameters. Lastly, citric acid as a green chelating agent is utilized to recover metal ions in the form of citrates and regenerate spent biosorbent along with detailed cost benefit analysis, thereby endorsing the circular economy approach.