Determination of the efficiency and removal mechanism of cobalt by crab shell particles

The effects of contact time, solution pH and ionic strength on interactions between cobalt ( 59 Co) ions in synthetic liquid waste and particles of raw crab shell, Portunus trituberculatus, in batch reactions were studied. Approximately 19.5mgdm −3 Co was removed within 6h after contact with 1.0gdm −3 crab shell at an initial concentration of 20mgdm −3 Co. Due to the dissolution of calcium carbonate in the crab shell, the solution pH changed spontaneously to 10, leading to precipitation of cobalt ions. The efficiency of cobalt removal depended on solution pH, but was less pH sensitive than for controls without crab shell. The maximum uptake of Co at an initial pH value of 5.0 was 510mgg −1 crab shell. The removal efficiency was affected slightly by ionic strength up to 2.0moldm −3 of NaCl. Scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) indicated that the removal mechanism of Co by crab shell resulted primarily from the dissolution of calcium carbonate followed by precipitation of cobalt on the surface of the shell. Compared with commonly used ion-exchange resins such as natural zeolite, Durasil 70, and Durasil 230, the efficiency of Co removal by a column of mixture of crab shell and activated carbon was at least three-fold greater, indicating that crab shell is a suitable biosorbent for the removal of cobalt from liquid waste.  2004 Society of Chemical Industry

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