Long-Term Lead Immobilization in River Sediment by Ca(OH)₂-Modified Rice Straw Biochar

Abstract

Remediation of lead pollution is of great significance to water and sediment, in which Pb plays an important role and is leading the way. Therefore, the control of lead pollution has become the most concerning environmental issue at present. Among many removal techniques for polluted river sediment, immobilization is a cost-effective remediation technology. Biochar (BC) derived from the straw stalk was developed based on the recycling of agricultural byproducts, and further, the biomass was treated with calcium hydroxide to obtain a modified biochar (BCC). The immobilization mechanism on Pb removal by BC and BCC was deeply investigated through combination with Pb(II)-targeted adsorption in aqueous solution. In addition, the immobilization effect was also evaluated by using the TCLP and modified TCLP (−28 days) methods for river sediment. The leaching concentration was beyond the Chinese criteria for hazardous waste (5 mg/L, GB5085−2007) after 18 h and it did not exceed the limit of 0.75 after 2 days for BCC, the performance of which is much better than that of BC. What's more, pH remained relatively stable (around 4.5 for BCC) in the whole leaching period. The composition of C-containing groups on the surface of the biochars showed that the weight of carboxyl groups was increased after modification (from 2.66 to 19.94%), whereas carboxyl groups were decreased after adsorption for Pb(II) (from 19.94 to 8.51% for the BCC). A series of batch studies suggested that metal adsorption by BC/BCC occurs by both chemical reduction and complexation processes that follow a Langmuir isotherm model (R 2 = 0.99) and pseudo-second-order kinetics (R 2 = 0.99). The adsorption results indicated that the maximum adsorption capacity of BCC was up to 913.0 mg/g. Therefore, the removal mechanisms of Pb(II) can be summarized as electrostatic attraction, cation exchange, and metal/functional group exchange reactions for a surface inner-sphere complex or coprecipitation.

Temperature-Dependent Adsorption Process of Neonicotinoid Insecticide Nitenpyram by Sawdust Biochar: Mechanism and Theoretical Simulation

“…The current research on biochar adsorbent is focused on its performance and application in wastewater treatment, but there is a lack of systematic research for preparing conditions, structure–function relationships, and theoretical simulation. , Therefore, it is significant and meaningful to study the pyrolysis temperature and size of biochar for the removal of neonicotinoid insecticides and to explore the molecular-level adsorption mechanism . In this study, sawdust biochar (SBC) was prepared via high-temperature pyrolysis, and the neonicotinoid insecticide nitenpyram (NTP) was used as the target pollutant to investigate the adsorption performance and mechanism of biochar.…”