Preparation Of Al-Mn-La Composite Metal Oxides And Their Removal Of Fluoride And Phosphate From Water

Anion pollution in water is becoming one of the biggest threats to China's water environment problems,excessive fluoride and phosphate in aqueous solution will pose a major threat to the aquatic environment and human drinking water safety.Among various treatment technologies,adsorption method has been extensively studied due to its cost-effective characteristics.The removal of pollutants depends on the performance of adsorbents.Metal oxides(such as Al,Mn,La,etc.)have become the focus of researchers in recent years due to their strong affinity for fluoride and phosphate.In the research work of this paper,firstly,the Al-Mn-(La)composite metal oxides material with or without 0.1M La were synthesized by co-precipitation method under different conditions of Al/Mn molar ratio,pH and calcination temperature.And the adsorption capacities of adsorbents to fluoride and phosphate was compared successively to obtain the suitable Al-Mn-(La)adsorbents for fluoride and phosphate removal.Then,two Al-Mn-La composite metal oxides were selected according to the difference of morphological structure and adsorption capacities of the products.and their adsorption effects and related adsorption mechanisms on fluoride and phosphate were systematically investigated.The main results are as follows:(1)Screening of materials for fluoride removal:The Al-Mn and Al-Mn-La adsorbents prepared at the conditions of Al/Mn 1:2,medium pH 8 and calcination temperature 100? had good fluoride removal performance,and they were named AM-1 and AML-1.AML-1 composite metal oxide had a stronger defluorination ability due to its smaller size,more unsaturated bonds on the surface,and more positive charges at low pH.Therefore.AML-1 composite metal oxide was selected as the adsorbent,and the adsorption of fluoride by AML-1 was systematically investigated.(2)Screening of materials for phosphate removal:The Al-Mn and Al-Mn-La adsorbents prepared at the conditions of Al/Mn 1:2.medium pH 10 and calcination temperature 100? had good phosphate removal performance,and they were named AM-2 and AML-2.AML-2 composite metal oxide had a stronger phosphate removal ability due to its uniform structure,a large number of pore structures,more unsaturated bonds on the surface,and more positive charges at low pH.Therefore.AML-2 composite metal oxide was selected as the adsorbent,and the adsorption of phosphate by AML-2 was systematically investigated.(3)Adsorption of fluoride by AML-1:The results showed that the adsorption of fluoride by AML-1 conformed to the second-order kinetic equation and had good adsorption effects in the pH range of 3-10.The adsorption of fluoride by AML-1 was spontaneous and endothermic.CO32-,SO42-and H2PO4-in aqueous solution could affect the adsorption of fluoride by AML-1,especially H2PO4-,which could significantly inhibit the fluoride adsorption.The maximum fluoride adsorption capacity of AML-1 was 48.08 mg/g(pH=7)and 121.95 mg/g(pH=3).AML-1 had general regeneration performance and was not suitable for multiple reuse.According to the experimental results and the analysis of FTIR and XPS before and after adsorption,electrostatic attraction and ion exchange might be the main mechanism of fluoride adsorption by AML-1.(4)Adsorption of phosphate by AML-2:The results showed that the adsorption of phosphate by the adsorbent conformed to the second-order kinetic equation and had good adsorption effects in the pH range of 3-7.The adsorption of phosphate by AML-2 was spontaneous and endothermic,and it was basically unaffected by other coexisting ions.The maximum adsorption capacity of AML-2 for phosphate was 50.00 mg/g(pH=7)and 109.89 mg/g(pH=3).AML-2 had good regeneration performance and could be reused.According to the experimental results and the analysis of FTIR and XPS before and after adsorption,electrostatic attraction and ion exchange might be the main mechanism of phosphate adsorption by AML-2.