Distribution and chemical partitioning of heavy metals in marine near-shore sediment cores: a case study from the Xugou, Lianyungang, China.

The concentrations and chemical partitioning of heavy metals (Co, Cr, Ni, Zn, Cu, and Pb) in the marine near-shore sediment cores were investigated. Typically, the mean concentrations from Core B sediment samples were 98.6, 21.1, 47.0, 46.4, 107.6, and 31.9 mg kg( - 1) for Cr, Co, Ni, Cu, Zn, and Pb, respectively. The heavy metal concentrations were normalized to commonly used reference elements Al, Li, Sc, and total organic carbon. Based on Pearson coefficients, Li was found to be a good normalizer for Co (r = 0.974), Cr (r = 0.967), Ni (r = 0.898), and Zn (r = 0.929) in 80 sediment samples from three sampling sites. However, the correlation coefficients between Li and Cu, and Li and Pb were relatively low. Multivariate statistic approaches (Principal Component Analysis and Cluster Analysis) were adopted for data treatment, allowing the identification of two main factors controlling the heavy metal variability in the sediments. Heavy metals in the enrichment sections were evaluated by a sequential extraction method for possible chemical forms in sediments. The results showed that the residual, Fe/Mn oxides and Organic/sulfide fractions were dominant geochemical phases in the enriched sections, indicating low bioavailability of heavy metals in sediments.

Removal of Cr (VI) with wheat-residue derived black carbon: reaction mechanism and adsorption performance.

The removal of Cr (VI) from aqueous solutions using black carbon (BC) isolated from the burning residues of wheat straw was investigated as a function of pH, contact time, reaction temperature, supporting electrolyte concentration and analytical initial Cr (VI) concentration in batch studies. The effect of surface properties on the adsorption behavior of Cr (VI) was investigated with scanning electron microscope (SEM) equipped with the energy dispersive X-ray spectroscope (EDS) and Fourier transform-infrared (FTIR) spectroscopy. The removal mechanism of Cr (VI) onto the BC was investigated and the result showed that the adsorption reaction consumed a large amount of protons along the reduction of Cr (VI) to Cr (III). The oxidation of the BC took place concurrently to the chromium reduction and led to the formation of hydroxyl and carboxyl functions. An initial solution pH of 1.0 was most favorable for Cr (VI) removal. The adsorption process followed the pseudo-second order equation and Freundlich isotherm very well. The Cr (VI) adsorption was temperature-dependent and almost independent on the sodium chloride concentrations. The maximum adsorption capacity for Cr (VI) was found at 21.34 mg/g in an acidic medium, which is comparable to other low-cost adsorbents.