Separation Of Al₁₃ Using Sulfate Precipitation And The Coagulation Behaviors Of Purified Al₁₃

Coagulant is one of the key factors affecting the efficiency of coagulationprocess. Alum is the most frequently applied traditional coagulat in the world.During the past decades, inorganic polymer flocculants (IPFs) have been developedrapidly and become applied widely. Among them, polyaluminum chloride (PACl) isone of the typical products and its efficiency is proved to be superior to thetraditional coagulations. In aqueous solution, Al(â…¢) exhibits strong trend ofhydrolysis. After dosiong into water, it will undergo serial hydrolysis,polymerization, aggregation and precitation. As results, various possible speciesexisting in metastable or transient state could be formded in the bulk solution, suchas monomers, oligomers, Al₁₃[AlO4Al12(OH)24(H2O)127+] and colloidal phase.Among them, the Al₁₃ species has been received more and more attention and isconsidered to be the most important species. Undoubtedly, finding the methods toseparate various species (especially Al₁₃) from the hydrolysed solution, and toinvestigate their structure and physicochemical properties is of significantimportance.In this study, pure Al₁₃ solution at medium high concentrations was perpared byusing SO4/Ba separation method. The effects of SO4/Al molar ratio and the initialtotal Al concentration on the precipitation reactions of sulfate with different Alspecies were investigated. The factors influencing the metathesis reaction betweensolid Al₁₃-SO4 and Ba(NO3)2 were evaluated. Results showed that high purity Al₁₃could be obtained at the medium Al concentration range of 0.4-0.6mol/L;the bestSO4/Al ratio was 0.6:1 for precipitation- separation of Al₁₃;Al₁₃-SO4 precipitateswere mostly consisted of tetrahedral crystals. During the metathesis reaction, Ba/SO4molar ratio of 1:1 was the optimal value. Small range temperature variation andultrasonic had no marked influence on metathesis reaction rate and final Al₁₃concentration. Higher initial Ba(NO3)2 concentration could result in higher Al13concentration accordingly. The purity of Al13 solution could be reached to 92.1%statistically.The transformation and stability of high concentration Al13 was dicussed. Themechanisms of hunmic acid removal by coagulation with AlCl3, comercial PACl,and purified Al13 were compared. Special attention has been paid on the aspects ofdifferent coagulation species. The influences of pH and dosage were examined bymeasuring the changes of zeta potential, residue turbidity (RT), and residue humicacid (HA). The results indicated that Al13 had much high speciation stability andcoagulation efficiency. Under the suspension systen containing HA, the change ofpH had less influence on the coagulation behavior of Al13 compared with the Al(â…¢)salt. The high charge neutralization ability of Al13 could also contribute to its uniquecoagulation features in both turbidity and organic matter removal.