Chemical characteristics of groundnut and sheanut shell biochars as adsorbents and soil conditioners in the era of ecological sustainability

This study investigated the influence of pyrolysis temperatures on characteristics of groundnut and sheanut shell biochars as potential adsorbents and soil conditioners. Groundnut and sheanut shell biochars were produced at pyrolysis temperatures of 350 ± 5 °C and 700 ± 5 °C using muffle furnace. The chemical characteristics of the biochars were analysed, potential contamination and ecological risk were determined based on the metal enrichment index and potential ecological risk index (PERI). pH values of the biochars ranged from 9.42 to 10.23 and 662.33 to 3206.67 μS/cm for electrical conductivity. The total compositions of carbon and nitrogen for GB350, GB700, SB350 and SB700 ranged from 58.13% to 70.23% and 0.45% to 1.37%, respectively. The minerals composition of GB350, GB700, SB350 and SB700 ranged from 12944.92 to 20873.30 mg/kg for potassium, 192.24 to 410.72 mg/kg for sodium, 3567.98 to 13451.83 mg/kg for calcium and 1150.33 to 3414.34 mg/kg for magnesium. The pH of the biochars is found to be alkaline which upsurge with increasing pyrolysis temperature. Concentrations of nutrients such as calcium, potassium, magnesium and phosphorus diverse in groundnut shells feedstocks due to the pyrolysis conditions. The groundnut and sheanut shell biochars can increase essential nutrients such as nitrogen, phosphorus, and potassium in soil, which are conducive to growth of plant. The availability of phosphorus in the biochars make it phosphorus-rich and can be used as slow-release fertilisers. The potential toxic metals in the groundnut and sheanut shell biochars have values that suggested low contamination and less potential ecological risk making the biochars ecofriendly. Groundnut and sheanut shell biochars can be used in fields as an adsorbent and a soil amendment based on its chemical characteristics.