A Study On The Characteristics Of Selective Complexation Between Humic Acids And Aluminum Sulfated

Humic acids is an organic pollutant which gets attention from the environment water field, The HA molecules include multi-oxygenous functional groups. With the help of financial assistance of the national science fund, the mechanism of reaction between the oxygenous functional groups of humic acid and Aluminum sulfated were studied systematically under different pH value.Making use of the fluorescence scanning and the quantitative analysis technique of mulberry dye fluorescence, the state of the complexation of humic acids with aluminium ions and hydrolysis was analyzed during the coagulation of HA with Aluminum sulfated as coagulants. The study showed that: with pH=2, complexation reaction could take place between HA and aluminum ions. As pH value increases gradually, the quantity of aluminum ions reacting with HA also grows accordingly. Especially, in pH=5, the intensity of the two reactants was greatest. But at pH ≥7, it is hard to take place the complexation reaction between HA and aluminum sulfated. The quantitative analysis technique of mulberry dye fluorescence revealed that, the residual Al³⁺ and the dosage of the coagulants kept a linear correlation under the low dosage at pH<7and pH≥7.According to the slope of linear, we can calculate the mol value of aluminium ions reacting with HA under the difference pH. The value present the peak shape at pH=5, so pH=5 is an optimum condition for the coagulation. At a certain coagulant dosage, the residual Al³⁺ decreases sharply. The hydrolysis of aluminum sulfated was monitored by applying photometric dispersion analyzer (PDA2000), it revealed that the coagulants have produced considerable amount of vague form of aluminum hydroxide. So the removal of HA is mainly caused by absorbing and sweep flocculating onto the precipitated hydroxides resulted from the coagulants hydrolysis. The mechanism of chemical reaction between humic acid and metal salts coagulant was discovered by NMR analyses. It indicated that the essential of coagulation of HA is the complexation between protons released from the HA molecule which contain carboxyl , hydroxyl , amidocyanogen with metal ion. Choosing four typical HA: chromatograph, zincon, fluorescein, folic acid, assisted by ¹H NMR we analyzed the rule of the proton transfer and their selective complexation with aluminum ions. It is shown that the proton transfer is affected by the compactness between metal ions with aluminum salts. It is easy for them to release the proton if the carboxyl, hydroxyl, amidocyanogen are linked by benzene and hard if they are in the hydrocarbon chains. The complexation of humic acids with aluminium coagulant is selective under different pH. The carboxyl, hydroxyl linked with benzene are easy to react with aluminum ions as well as their hydrolyastes, which is not affect by pH value as the amidocyanogen only react selective complexation with aluminum ions in low pH. The reaction between carboxyl, hydroxyl, amidocyanogen in hydrocarbon chains with aluminum ions is influenced by pH seriously, and is selective. In low pH, carboxyl and hydroxyl react with aluminum ions hardly, the higher the pH, the easier the reaction is while amidocyanogen has opposite characteristic.