Overcoming heavy metal pollution from nickel mining wastewater in Indonesia using green chemistry activated rice husk biochar for sustainable remediation

As the world's leading nickel producer, Indonesia faces significant environmental challenges, particularly related to mining waste containing heavy metals such as Ni, Cu, and Zn.While conventional chemical methods are often used, they are expensive, hazardous, and unsustainable.Therefore, this study aims to review and synthesize the current knowledge on the utilization of rice husk biochar, activated with green chemistry principles, as an effective and sustainable remediation solution.This approach was chosen because rice husk biochar is an abundant and inexpensive biomass in Indonesia, with high porosity and functional groups efficient in heavy metal adsorption.The findings indicate that rice husk biochar activated using green chemistry methods (e.g., citric acid, FeSO, or KOH) exhibits high adsorption capacity, with some studies reporting capacities up to 384.62 mg/g for Pb(II) and removal efficiency for Cu up to 96.02%.Furthermore, the biochar shows good stability with metal release rates of less than 1% and can be regenerated for up to 4-5 cycles, recovering 60-85% of its initial capacity.Nevertheless, this review identifies several significant limitations, such as the lack of studies on real mining waste application, long-term regeneration testing, and metal recovery from saturated biochar, all of which are crucial for circular economy implementation.This work has high originality and significance as it specifically highlights biochar from rice husks and emphasizes green chemistry principles.Practically, the use of this biochar offers an environmentally friendly and economical alternative for managing mining waste in Indonesia.