As (V)/Cr (VI) pollution control in soils, hemp waste, and other by-products: competitive sorption trials

Environmental Science and Pollution Research

DOI: 10.1007/s11356-016-7108-0

We study As(V)/Cr(VI) competitive sorption on a forest soil, a vineyard soil, pyritic material, mussel shell, pine bark, oak ash, and hemp waste, adding variable As(V) and Cr(VI) concentrations or displacing each pollutant with the same concentration of the other. When using variable concentrations, As(V) showed more affinity than Cr(VI) for sorption sites on most materials (sorption up to >84 % on oak ash and pyritic material). The only exception was pine bark, with clearly higher Cr(VI) sorption (>90 %) for any Cr(VI)/As(V) concentration added. Regarding the displacement experiments, when As(V) was added and reached sorption equilibrium, the subsequent addition of equal Cr(VI) concentration did not cause relevant As displacement from oak ash and pyritic material, indicating strong As bindings, and/or low competitive effects. When Cr(VI) was added and reached sorption equilibrium, the subsequent addition of equal As(V) concentration caused Cr(VI) displacement from all materials except pine bark, indicating weak Cr bindings. In view of these results, oak ash and the pyritic material could be used to remove As(V) in concentrations as high as 6 mmol L−1, even in the presence of a wide range of Cr(VI) concentrations, whereas pine bark could be used to remove Cr(VI) concentrations as high as 6 mmol L−1. The other materials assayed (including hemp waste, studied for the first time as As(V) and Cr(VI) bio-sorbent) cannot be considered appropriate to remove As(V) and/or Cr(VI) from polluted media.

Cr(VI) sorption/desorption on pine sawdust and oak wood ash

International Journal of Environmental Research and Public Health

DOI: 10.3390/ijerph120808849

The objective of this work was to study Cr(VI) sorption/desorption on two by-products from the wood industry: pine sawdust and oak wood ash. The retention/release experiments were carried out using standard batch-type trials. In the sorption-phase experiments, pine sawdust showed 23% sorption when a concentration of 100 mg Cr(VI)·L-1 was added, whereas sorption on oak wood ash was 17%. In the desorption-phase, chromium release was clearly higher from pine sawdust than from oak wood ash (98% and 66%, respectively). Sorption curves were well fitted to the Freundlich and Lineal models. In view of the results, both materials can be considered of very limited value to remove Cr from polluted soil and water, which can be of relevance regarding its appropriate use as biosorbents and recycled by-products.