Valorization of invasive plant and leaf litter wastes into biochar: Production, properties and potential for arsenic removal

Arsenic (As) is an emerging pollutant and because of its toxicity, long-term persistence, elevated mobility, and high bioavailability, it has contaminated groundwaters of countries including India, China, and USA. Recently, biochars have emerged as a promising method for remediation of As. In the present study, biochars were prepared from invasive plants and leaf/plant litter waste at 300-700 degrees C temperatures. Further, the study assessed the impact of these feedstocks on physico-chemical properties and As removal efficiency of biochars. Based on high yield and As removal efficiency, the ones produced at 500 degrees C (LCB500 for Lantana camara-based biochar and LLB500 for leaf litter-based biochar) were chosen for advanced functional, morphological, and parameter optimization studies. Biochars showed a porous surface with high stability, mineral content, and surface functionality. Batch adsorption studies showed As adsorption capacity of 5.47 mg g(-1) for LCB500 (at 4 mg L-1 initial concentration, 0.6 g L-1 dosage, 25 degrees C, 90 min contact time, and pH 8) and 6.36 mg g(-1) for LLB500 (at 6 mg L-1 initial concentration, 0.8 g L-1 dosage, 25 degrees C, 90 min contact time, and pH 7). Emergence and disappearance of peaks in FTIR spectra and XRD diffractograms and isotherm, kinetic, and thermodynamic studies indicated a favourable multi-layer As adsorption with participation of both physisorption and chemisorption. Under optimized conditions, biochars showed removal of >75% As from As-contaminated groundwater samples collected from Sahibganj (Jharkhand). The recycling of spent LCB500 and LLB500 showed high reusability up to five cycles. Meanwhile, inconsequential impacts of co-existing ions were observed, indicating substantial efficacy for practical environmental applications. Cost analysis demonstrated considerable techno-economic feasibility and promotion of circular economy via development of value-added products through utilisation of waste. The present study recommends valorization of invasive plants and leaf litter wastes into sustainable biochars which could be used for effective removal of As from groundwaters.