Applications of a carbon sorbent for the recovery of metals from waste waters

This paper is concerned with the preparation and characterisation of a novel carbon sorbent derived from flax shive (linum usitatissimum) a waste product of the fibre industry. The sorbent possesses both ion exchange and redox properties the latter providing a major advantage in the removal of polluting heavy metal ions. An additional advantage is that the sorbent maintains its fibrous nature so is well suited to column operation as a low-pressure drop is found over the column bed. Experiments are described on the sorption of cadmium and mercury to determine the underlying reaction processes involved. The sorption of cadmium follows an ion exchange process whereas the removal of mercury(II) from chloride media is much more complex. In this case, following the normal loading to the extent of the ion exchange capacity, the sorbent reduces the mercury(II) ions to insoluble mercury(I) chloride or metallic mercury thus regenerating the ion exchange capacity. The process can therefore be repeated many times leading to potential removal capacity of mercury greater than 1 gram mercury/gram sorbent.