Hydroxyapatite-activated seaweed biochar for enhanced remediation of fluoride contaminated soil at various pH ranges

Abstract

This study investigated the defluoridation efficiency of hydroxyapatite-activated seaweed (Eucheuma Cottonii) biochar (HSB) at various soil pH ranges (3–11) while monitoring the impact of contact time (30 min - 2.5 h), adsorbent dosage (0.1–0.5 g) as well as the initial fluoride concentration and compare its performance to its respective seaweed biochar (SB). Activation of SB with the hydroxyapatite lead to a shift in its point-zero-charge (pHPZC) from 6 to 7.4 broadening its defluoridation pH range from a solitary 5 to amid 3 through 11. The fluoride adsorption mechanism was found to follow both Langmuir (R2 = 0.956) and Freundlich (R2 = 0.942) isotherm models with a maximum defluoridation capacity of 3.03 mg/g equivalent to the defluoridation efficiency of 79%. This is accounted to the existence of soil ions, SB active sites, and the attached hydroxyapatite, as fluoride adsorption sites each exhibiting a dissimilar fluoride removal mechanism. Therefore, the HSB could be a promising adsorbent for fluoride removal in the fluoride contaminated agricultural soils of inclusive pH ranges.