Solidification and Stabilization of Spent Pine-cone Biochar using Chemically Bonded Phosphate Cement

Abstract

Spent biochar is produced after adsorption of heavy metal which is hazardous by nature. A suitable disposal technique is required to prevent the leaching of heavy metals from spent biochar into the environment. This study highlights the solidification and stabilization (S/S) of copper loaded spent pine-cone biochar by chemically bonded phosphate cement (CBPC). The response surface methodology (RSM) was used to conduct S/S experiments in order to evaluate the compressive strength of CBPC products. The CBPC samples were prepared by varying biochar content (5-50 wt. %); W:S (0.15-0.3) and curing time(3-28d). Results illustrated that CBPC products containing biochar had higher compressive strength upto 12.8 MPa in comparison to CBPC without biochar i.e., upto 10.8 MPa. XRD and SEM analysis confirmed the presence of K-struvite (MgKPO4.6H2O), copper containing phases (Ca-Cu-Si), copper phosphate precipitates (Cu3(PO4)2) and filling of pore spaces by spent biochar. Highest compressive strength of 12.8 MPa was obtained at an optimized biochar content of 25%, W:S of 0.18 and curing time of 28 d. The evaluation of leaching potential by TCLP illustrated that stabilization of Cu (II) upto 99.9% was achieved in CBPC product. The risk assessment study revealed that there is no significant danger due to leaching of heavy metals from final CBPC product indicating that it can be readily disposed in the hazardous landfill sites.