Bioavailability and Leaching of Cadmium from Biochar-Amended Contaminated Soil

Abstract

Cadmium (Cd) is a heavy metal that can be dangerous to all living things and has long-lasting resistance to the environment. These metals can enter farming land due to their dissociation from soil minerals in effluents, mining waste, and landfills. The most frequently used adsorptive materials and precipitating reagents are commonly utilized to reduce the mobility and bioavailability of heavy metals. As an adsorbent, biochar may absorb heavy metals in the soil while also enhancing soil productivity. Biochar has been utilized successfully to lessen heavy metal accessibility and leaching in contaminated soils. The purpose of this study was to determine the effect of sawdust biochar on soil properties at two distinct temperatures and to assess the impact of biochar on soil Cd contamination. In this experiment, sawdust biochar was pyrolyzed at two temperatures, namely, B-450 (450 ◦C, 2 hrs) and B-550 (550 ◦C, 1 hr), to treat the contaminated soil with Cd. B-450 and B-550 were properly mixed separately with 750 g of contaminated soil with Cd concentrations of 0% (T1), 1.25% (T2), 2.5% (T3), and 5% (T4) (w/w). Each unit sample was replicated four times. The samples were set up in a Factorial Completely Randomized Design (CRD) and incubated at 52% field capacity for 60 days. According to the results, the addition of B-450 and B-550 enhanced the soil pH, soil EC, and soil CEC of the polluted soil. The rise in pH and CEC of the soil increased Cd adsorption due to an increase in adsorption sites. The levels of water leachable Cd reduced dramatically as the rate of biochar application increased. The soil treated with 5% B-550 had the lowest leachable Cd level due to the high exposure of the inner pores and their functional groups. B-550 can absorb heavy metals more effectively than B- 450 in Cd-contaminated soil because of its high surface area and pH. Biochar produced at higher temperatures may also provide more CEC. Increased CEC of biochar would improve the soil particle’s capacity to absorb heavy metals. As a result, the B-550 could be suggested for the reclamation of heavy metal-contaminated soil, and a biochar pyrolyzed at higher temperature can be used rather than a biochar pyrolyzed at lower temperature to achieve these goals.