Adsorption characteristics of Pb²⁺ on natural black carbon extracted from different grain-size lake sediments

As a major organic component in aquatic sediments, black carbon (BC) could act as super surface sorbent for contaminants in soils or sediments due to its relatively structured carbon matrix with high degree of porosity and extensive surface area. In this work, the adsorption characteristics of Pb²⁺ were studied using BCs as adsorbents, which were extracted from four particle sizes of sediment from Lake Wuliangsuhai (WLSH), under conditions of different pH, BC content, and ionic strength. The results showed BC content near to 1 % of sediments from WLSH, in which BC1, BC2, BC3, and BC4 composited about 1.8, 1.6, 1.1, and 0.8 % in the sediment fractions of >180, 180-63, 63-32, and <32 μm, respectively. The specific surface area and the Pb²⁺ sorption capacity were increased with decreasing the particle size of BCs. Correspondingly, the adsorption percentage of Pb²⁺ increased with increasing initial pH and BC content but declined as the increase of ionic strengths. The Pb²⁺ sorption capacity was reached maximum at pH 5-6. Compared pre- to post-sorption BCs by SEM-EDS and FTIR, although the carboxyl (C=O) and phenol (OH) groups on BC fractions contributed to Pb²⁺ sorption, the main adsorption mechanism of BCs was the surface sorption at pH <6. Relatively, the contribution of BCs accounted for about 18 % of Pb²⁺ sorption capacity on sediments. This work is helpful to understand the environmental effects of different size fractions BCs extracted from natural sediments.