Modification of biochar with magnesium compound for phosphorus removal and lead immobilization in soil / Nurul Fariha Mohd Idrus

Biochar converted from carbon-rich wastes and modified with magnesium (Mg) provide method on solving Phosphate pollution through struvite precipitation. In this study, laboratory experiments were conducted to optimize the modification parameters of Sawdust Biochar (SD) modified with two types of magnesium (i.e. MgCl2 and MgO2) for phosphorus (P) recovery to produce Mg-impregnated biochar (i.e. MC300 and MO700). After P removal using MC300 and MO700, samples were further modified with Phosphate from artificial human urine (AHU) to offer an alternative approach for treating Lead (Pb) contaminated soils. The parameters that has been optimized for producing MgCl2 modified biochar (MC300) and MgO2 modified biochar (MO700) with the highest P sorption capacity were concentration of AHU, optimum dosage of biochar, temperature pyrolysis of biochar, contact time and concentration of Mg. To characterize the physical and chemical properties of MC300 and MO700, CEC, elemental analysis, SEM-EDX, BET analysis, FTIR and TGA analysis were done for the entire samples. To study the immobilization of Pb in soil with biochar, leaching test (i.e. below 1.69 mg/L of Pb concentrations) and selective sequential extraction (i.e. decreased exchangeable Pb to 9% and 0% respectively.) were done using P modified biochar (i.e. P300 and P700). To support the result of study, isotherm and kinetic studies were investigated. MO700 have the highest sorption capacity for total P (i.e. 9554.20 mg/g) compared to MC300. Next, the contact time for MC300 and MO700 were 80 min and 120 min respectively. The optimum sorbent/solution ratio were 0.1g/L and the optimum mg concentration used to modify biochar (i.e. B300 and B700) were at 5% w/v. Adsorption isotherm for Phosphorous indicated that adsorption process of MO700 happens on a heterogeneous surface by several layer adsorption mechanism while MC300 happens on homogenous bound number of active site. Kinetic study results suggesting that the entire adsorption process for both MC300 and MO700 were better described by chemisorption process. For the characterization by SEM-EDX analysis showed after undergo pyrolysis to formed B300 and B700, the surface morphology has more pores formed on its surface compared to raw sawdust. The blue colour on the surface of the particles by the spot EDX analysis indicates the presence of Magnesium on the surface of the MC300 and MO700. For struvite biochar (P300 and P700), it can be seen that a small crystal called struvite were seen to formed on the surface and the presence of P in the EDX analysis. Other than that, BET study proved that high pyrolysis temperature gives better surface area for B700 but decrease surface area for MO700. From FTIR analysis, functional groups of P-O stretching vibration, aromatic C-H, NH2 stretching bands, C=C alkene, C=O amide, C=C aromatic ring, and C=N aromatic ring were mainly involved in the Mg and P adsorption. Lastly, for TGA results, there are four different mass loss phases that has been separated by the lines for specific temperature intervals. For the biochar sample, the first decomposition stage happened to all the samples at < 300 °C.There were two decomposition stages between 250°C and 350°C at phase 2 that correspond to the sharp peak of DTG at 350°C for both MC300 and MO700. Lastly, stage 3 and 4 at 450°C and 800°C, respectively were attributed to the slow decomposition of residual solids. This study cover the findings of gap, between the modification of biochar with two different source of Mg and Phosphate removal using Mg biochar that may immobilize Pb in soil that can contribute to the greening and reclamation of soil and river. This study is important for future research that will contribute way forward in the area of nature restoration.