Research On The Role Of Low Molecular Weight Organic Acids On Kaolinite Dissolution

In order to know better the effect of low -molecular -weightorganic acid (LOAs) in soils in the processes of red soil acidification, the experimentwas conducted to evaluate the role of several kinds of LOAs ( citiric acid, oxalic acidand malic acid) on the dissolution and base cation activation of kaolinite with batchmethod. The result showed as follows:1) Solvability of kaolinite was enhanced with an increase in the concentration and acidity of LOAs. Moreover in general, the solvability of LOAs on kaolinite were biggerthan proton (HAC).2) When the acidity of LOAs wasn't adjusted, LOAs promoted the kaolinite solvability in the order oxalic acid > citric acid > malic aicd; However in HAC/NH4AC buffer solution, the ability that LOAs promoted the kaolinite dissolution had relation to the concentration and acidity of LOAs, when the concentration of LOAs was 1mM, LOAs promoted the kaolinite solvability in the order oxalic acid > citric acid > malic aicd (pH3.5) and citric acid > oxalic acid > malic acid (pH4.5 and pH5.5 ); However, when the concentration of LOAs was as big as or bigger than 5mM, the order was oxalic acid >citric acid >malic aicd.3) When the acidity of malic acid wasn't adjusted, Si was preferentially released compared to Al, but in HAC/NH4AC buffer solution, the malic acid resulted in the preferential release of Al; However in respect of citric acid and oxalic acid, no matter if the acidity was adjusted, Al was both preferentially released compared to Si. In general, in citric acid and oxalic acid solution, kaolinite nearly dissolved congruently in reactive metaphase or anaphase; In malic acid solution, stoichiometry of kaolinite dissolution is complex. 117低分子量有机酸对高岭石溶解作用的研究4) LOAs could promote the release of K+, Na+, Ca2+, Mg2+ from kaolinite, even if the concentration of LOAs was very low (100μM). But the effect of the concentration of LOAs on the release of base cation from kaolinite was complex.5) The reaction order(nH) and rate constant(kH) of kaolinite dissolution in HAC/NH4AC buffer solution were 0.28 and 1.12×10-12 respectively; when the concentration of citric acid , oxalic acid and malic acid was 1mM. The reaction order(nH ) were 0.09, 0.27 and 0.18 respectively,the rate constant (kH ) were L L 4.03×10-13, 2.62×10-12 and 4.73×10-13 respectively；when the concentration was 5mM, The reaction order(nH ) were 0.16, 0.37 and 0.16 respectively,the rate L constant (kH ) were 1.38×10-12, 2.32×10-11 and 4.97×10-13 respectively； when L the concentration was 10mM, The reaction order(nH ) were 0.18, 0.34 and 0.16 L respectively,the rate constant (kH ) were 2.17×10-12, 2.60×10-11 and 6.05×10-13 L respectively.6) The ability of Ligand-promoted kaolinite dissolution was related to reactive solution acidity and the kind of LOAs. In citric acid solution, when the concentration of citric acid was bigger than 1mM, the enhance of solution acidity availed the increase of Ligand-promoted kaolinite dissolution,however when the concentration of citric acid was no more than 1mM, the enhance of solution acidity possibly restrained the ability of Ligand-promoted kaolinite dissolution. In oxalic acid solution, the enhance of solution acidity availed the increase of Ligand-promoted kaolinite dissolution. But In malic acid solution, when the concentration of malic acid was 10mM, the enhance of solution acidity availed the increase of Ligand-promoted kaolinite dissolution, however when the concentration of malic acid was 1mM and 5mM, the enhance of solution acidity possibly restrained the ability of Ligand-promoted kaolinite dissolution. Ho...