Lead immobilization in simulated polluted soil by Douglas fir biochar-supported phosphate. (April 2022)

• Record Type: Journal Article
• Authors: Beatrice, Arwenyo; Varco, Jac J.; Dygert, Andrew; Atsar, Felix S.; Solomon, Sabrina; Thirumalai, Rooban Venkatesh K.G.; Pittman Jr., Charles U.; Mlsna, Todd
• Is Part Of: Chemosphere. Volume 292(2022)
• Publication Date: 2022-04
• Subjects: Heavy metals -- Biochar supported-phosphate -- In-situ-immobilization -- Bioavailability -- Soil pollution; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2021.133355
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: This study compared the lead (Pb 2+ ) immobilization efficacy of biochar-supported phosphate to conventional in-situ heavy metal immobilization methods (with lime, neat biochar and phosphate). The biochar-supported phosphate was obtained by treating Douglas fir biochar (BC) with anhydrous calcium chloride and potassium dihydrogen phosphate. The amount of Pb 2+ immobilized was determined by comparing the concentration of ammonium nitrate extractable Pb 2+ lead from lead-spiked soil (without amendment) to that of a 30 d incubation with (a) lead-spiked soil plus 5% (wt./wt.) biochar supported-phosphate, (b) lead-spiked soil plus 5% (wt./wt.) untreated Douglas fir biochar, (c) lead-spiked soil plus 5% (w/w) lime and (d) lead-spiked soil plus 5% (wt./wt.) potassium dihydrogen phosphate. The control (lead-spiked soil without amendment) produced the largest quantity (96.08 ± 9.22 mg L −1 ) of NH4 NO3 -extractable Pb 2+, while lead-spiked soil treated with 5% (wt./wt.) biochar-supported phosphate resulted in the lowest quantity of NH4 NO3 extractable Pb 2+ (0.3 ± 0.2 mg L −1 ). The mechanism for immobilization of Pb 2+ by BP occurs at pH < 7 through dissolution of hydroxyapatite embedded in BP during modification, followed by precipitation of insoluble Pb10 (PO4 )6 (OH)2 . The residual lead fraction in the lead-spiked soil increased by 20.9% following amendment with BP. These results indicate that biochar-supported phosphate is a candidate to reduce lead mobility (bioavailability) in polluted soil. This amendment may lower Pb 2+ uptake into plants while minimizing the potential for water contamination due to Pb 2+ mobility. Graphical abstract: Image 1 Highlights: Biochar-supported phosphate (BP) effectively immobilized Pb 2+ from polluted soil. A 1% dose of BP removed 87% of the extractable Pb 2+ originally present within 10 d. Pb 2+ react with C a 10 ( P O 4 ) 6 ( O H ) 2 to precipitated P b 10 ( P O 4 ) 6 · ( O H ) 2 in soil at pH < 7. After amendment with 5% BP, the residual (immobilized) lead increased by 20.9%.