| With rapid development of industry, environmental pollution became more and more serious. Heavy metals are major resources of pollutants. These metals could be accumulated in organisms (including humans) through the food chain, and then do harm to human body. There are many different physical or chemical methods to remove metal pollutants from liquid waste when these metals are present in high concentration. since such methods as precipitation, evaporation, electroplating, ion exchange and membrane processes not only cost expensively, but also are unsatisfactory for removing such contaminants at very low concentration, even possibly make secondary environmental pollution, this has led to an increasing interest in the application of biosorption technology which is comparatively cheaper for the removal of trace amounts of toxic metals from dilute aqueous solutions.The accumulation of metals by algae, bacteria, fungi, and yeasts has been extensively studied and its application in the treatment of metal water was well documented. Of these studies, algae gained increasing attention due to the fact that not only the resource of algae is rich, but also algae are relatively cheap to be processed and able to accumulate high metal content. Mariculture is thriving all over the world, especially in Asia. More recently, it has been found that Spirulina could be adapted to grow well in seawater, thereby saving valuable farm land and expensive culture medium. However, metal ions adsorption by Spirulina has been rarely studied. The lack of information concerning Spirulina adsorption warrants detailed studies. In this paper, microalga Spirulina maxima was chosen for four metals accumulation studies. The objective was to study the effects of environmental transformation on metal-algae interactions and the mechanisms of metals adsorption by Spirulina maxima. The conditions of adsorption were tested by using batch tests. The role played by various functional groups in the cell wall of Spirulina maxima in adsorbing metal ions was investigated by using infrared spectroscopy and chemical treatment to modify the functional groups. Results were as follows:Many metals ions could be adsorbed by Spirulina maxima. Under the condition of pH5.5, 2h contact time, 50mg/l of the metal ions concentration, 2g/l biomass, the absorption ability of the alga from high to low was silver, lead, zinc, copper, manganese and nickel. The value of pH would have significant effect on the metal ions uptake by Spirulina maxima . The amount of metal biosorption was comparatively little when the value of pH was less than 3, and increased with pH rising. When pH ≥4, the amount of lead, cadmium and copper ions adsorption did not increased with rising of pH. The amount of zinc adsorption increased while the value of pH ranged from 2 to 6.The biomass of Spirulina maxima pretreated by CaCl2 would have different influences on the following four metals uptake. The amount of lead adsorption by raw spirulina mixama was less than that by pretreated biomass. There were no significant differences between raw and pretreated biomass adsorbing cadmium or copper. The amount of zinc adsorption by raw biomass was more than that by pretreated biomass. When the quantity of the biomass was increased, the adsorption amount reduced and the adsorption ratio added. Equilibrium isotherms of Freudlich for raw and pretreated biomass adsorbing metal ions were obtained from batch adsorption experiments. The intensity of Spirulina maxima adsorbing metal ions from high to low was lead, cadmium and copper in turn under the same conditions.There was a phase of rapid ions uptake in the first fifteen minutes of contact, followed by a period of slow ions uptake. Above 70% of metal ions uptake occurred at the phase of rapid ions uptake . Three desorbing agents EDTA, HNO3 and Sodium citrate were used in the ions desorption. All three desorbing agents were considered efficient on cadmium desorption , and sodium citrate couldn't desorb lead well. Po...
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