Efficient Aluminum Speciations In The Systems Of Bloomed Microalgae Coagulated By Al-modified Clays

Red tide is an ecological disaster caused by the abnormal proliferation of microbial community.Frequently occurring red tides had caused profound and deleterious effects on coastal ecosystems and were capable not only of threatening offshore ecosystems and seriously affecting aquaculture,marine fisheries,tourism and other industries but also of endangering human health.The modified clay(MC)technology is one of the most widely used methods in the emergency management of red tide because it has the advantages of high algae removal efficiency,low-cost,no secondary pollution and extensive use.The aluminum-based modified clay(Al-MC)is a safe and efficient red tide control agent that has been studied and applied worldwide.Although it is well known that the distribution of hydrolytic aluminum species in aluminum flocculant affects its flocculation,little is known about the influence of particulars aluminum species on the micro-algae removal efficiency of Al-MC;this lack of knowledge creates a bottleneck in the development of more efficient Al-MC.Therefore,this study discussed from the following four parts:(1)The analysis method of aluminum species in the system of micro-algae removal by Al-MC was optimized.On the basis of selecting Al-Ferron method as the main method in this study,the applicability of Al-Ferron method in the system of removing micro-algae with Al-MC was discussed.The results shown that Mg²⁺in seawater has the ability of complexing with Ferron,which lead Mg²⁺to be the obstacle to the accurate application of Al-Ferron method.Therefore,parameter correction method was chosen to remove the influence of Mg²⁺.At the same time,according to the objective and particularity of this study,the classification in the traditional Al-Ferron method was optimized.The high-polyaluminum defined in traditional classification of Al-Ferron method was redefined into three parts:high-polyaluminum,particle aluminum and sedimentary aluminum.The optimized Al-Ferron method not only remain the advantages of convenient,quick and accurate,but also makes Al-Ferron method meet the requirements of this study.(2)The concentration of different forms of aluminum in the micro-algae removal by Al-MC was quantitatively analyzed,and the kinetic changes were investigated.Firstly,the dynamic change characteristics of aluminum morphology during micro-algae removal by aluminum chloride modified clay(AC-MC)and polyaluminum chloride modified clay(PAC-MC)were quantitatively characterized.It was found that aluminum desorbed from clay and existed in the system as the form of dissolved aluminum,and the dissolved aluminum in AC-MC had obvious hydrolytic flocculation phenomenon.In addition,the aluminum stably adsorbed on the clay exists in the form of particle aluminum,and is continuously flocculated and sedimentation with the process of micro-algae removal,and is transformed into sedimentary aluminum.(3)Based on the analysis results of the effective aluminum form of micro-algae removal by Al-MC,an optimization method for the preparation of PAC-MC was proposed.First,modified clay?-PAC-MC was prepared by insertion method for high particle aluminum(Al_p)content and without dissolved aluminum.Then,the modified clay?-PAC-MC was compensated by adding aluminum salt with high mononuclear aluminum(Al_a)content.The removal efficiency of?-PAC-MC prepared by the optimized two-step method was 10-15%higher than that of t-PAC-MC prepared by the traditional method.Preliminary analysis showed that the removal capacity of?-PAC-MC and?-PAC-MC was significantly correlated with the aluminum speciation distribution of red tide microalgae.(4)The mechanism of the difference of algae removal efficiency between Al-MC prepared by two-step method and traditional method was explored.Al_aand Al_pwere the dominant aluminum forms in both AC-MC and PAC-MC in the traditional preparation method of t-Al-MC.The concentration of Al_ain AC-MC is higher and it has better stress and algicidal ability.In PAC-MC,Al_aformed by adsorption of the macromolecule Al₁₃in PAC has excellent neutralization and bridging flocculation ability.In the Al-MC obtained by the optimized preparation method,?-PAC-MC relies on the electric neutralization of particle aluminum Al_pto remove microalgae,but the flocculation induced by flocculation has poor sedimentation performance.?-PAC-MC has both high concentration of Al_aand high flocculating ability of Al_p,and improved the floc sedimentation performance,has a better ability of algae removal.In conclusion,the aluminum analysis method suitable for the micro-algae removal by modified clay was firstly constructed in this study.Through the quantitative characterization of the distribution and change of aluminum form in different Al-MC removal processes,the mechanism of removing microalgae by aluminum modified clay was analyzed from the perspective of aluminum form.Based on the mechanism of removing algae from Al-MC,the optimization method of traditional preparation of modified clay was put forward from the perspective of improving the utilization rate of the external aluminum,and more efficiency Al-MC was obtained,which provided theoretical guidance for the subsequent development of Al-MC.