| Algae adsorption of heavy metal has been researched widely at home and abroad. But most of the researches focuse on the seaweed, researches about freshwater micro algae are less relatively. Researches often focus on the nonliving algae and immobilized algae powder. Actually, the freshwater micro algae resources is vast and has lots of advantages, for example, economical, non-toxic, easy to cultivate. Therefore, this research studied the characteristics and mechanisms of heavy metal adsorption by living micro algae.By screening, this study found that Nosloc sphaeroides Kutzing had strong adsorption of Cd2+. So Nosloc sphaeroides Kutzing was used as the research object to explore the characteristics and mechanism of the adsorption of heavy metal by fresh micro algae.This article examined the adsorption of six kinds of common heavy metal by Nostoc sphaeroides Kiitzing, namely Cu2+, Cd2+, Cr3+, Pb2+, Ni2+, Mn2+under multiple reaction systems. By comparing the adsorption quantity under different systems, we got that Nostoc sphaeroides Kutzing had strong adsorption capacity of Pb+. When the operating conditions were controlled:initial concentration of lOmg/L, pH 5.0 at 25℃, the Pb2+ adsorption were found to be 25.75±2.04mg/g under the condition of single heavy metal existence; the Pb2+adsorption were found to be 15.98±1.22 mg/g under heavy metal coexistence; the Pb2+ adsorption were found to be 1.077±0.03mg/g when the heavy metal initial concentration was 10mg/L. Comparing with the adsorption quantity under single heavy metal, the adsorption quantity decreased only 25.83±2.97% and 7.41±7.25% under the condition of heavy metal coexistence and other cationic coexistence, we got that Nostoc sphaeroides Kiitzing adsorbed of Cr3+ selectively.This study mainly explored the effects of time, initial concentration of heavy metal, temperature and pH on the adsorption of Pb2+, Cr3+. The results showed the adsorptions of Pb2+, Cr3+ by Nostoc sphaeroides Kiitzing were fast. When reaction was carried out for 10 minutes, the adsorption of Pb2+ had reached equilibrium; Adsorption of Cr3+ reached equilibrium when reaction was carried out for 20 min. Peudo-second-order dynamic model were more suitable for the adsorption. The adsorption enthalpy of Pb2+, Cr3+ by Nostoc sphaeroides Kiitzing were 41.03kJ/mol and 72.42kJ/mol. So the adsorptions were endothermic reactions. Removal rate of Pb2+ kept more than 90% when pH ranged from 4.5 to 6.5. Removal rate of Cr3+ kept more than 85% at pH=5-6.Adsorbent reaction could be fitted with adsorption equation. The Langmuir and Freundlich adsorption isotherm models were the most commonly used.The Freundlich adsorption isotherm was more suitable for describing the adsorption of Pb2+by Nostoc sphaeroides Kutzing (R2=0.9165). The dsorption of Pb2+ happened easily (n=0.6760<2). Adsorption of Cr3+ was more suitable for Langmuir adsorption model (R2=0.9829) fitting out the maximum adsorption capacity of 22.4215mg/g. The adsorption was the single molecule layer.Then article studied the mechanisms of the adsorption of heavy metals by Nostoc sphaeroides Kutzing with FTIR, Scanning electron microscopy and Energy Dispersive X-Ray Spectroscopy (SEM-EDX). Amino and hydroxyl were the main functional groups involved in the adsorption process and might occur complextion reaction with heavy metal. The adsorption process occurred ions exchange.This study using living algae provided a certain theoretical support for heavy metal wastewater trwatment. Nostoc sphaeroides Kutzing was suitable for growing in paddy fields, so it could be used to control the heavy metal pollution in paddy fields. Nostoc sphaeroides Kutzing had been intaked by humans because of its special nutrition in all ages. Through this study, we got that there were safety risks to intake Nostoc sphaeroides Kutzing growing in heavy metal pollution water. |
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