Biosorption of divalent heavy metal ions by rice husk: A review

Heavy metal carrying effluent from various industries is a major source of pollution nowadays. Biosorption of such heavy metals by agricultural lignocellulosic waste has been proven to be an efficient, low cost and environmentally viable separation method. This review mainly focuses on biosorption of heavy metals by natural or chemically and thermally modified rice husk. Rice husk is a very competitive sorption agent due to its availability, effectiveness and applicability for the removal of a wide range of heavy metals including Cd, Pb, Zn, Cu, Co, Ni which are considered to have higher environmental and resource depletion impacts. This chapter provides detailed and systematic review on the impacts of different parameters including pH, contact time, metal dose, sorbent dose, particle size, type of modifier and temperature on heavy metal sorption capacity of rice husk. Studies on kinetics and thermodynamics of sorption, equilibrium sorption models, column operation, and mechanism of sorption, elution and sorbent recovery have also been reviewed. Moreover, future research directions were recommended to avoid duplication of efforts and options for the development of industrial scale agri-waste based sorption column were proposed