| Scientific researches and production practice had been proved that aluminum sulfateaccelerated the Accumulation of organic matter on soda salt-alkalinized soil. In order to revealthe improvement effect of aluminium sulfate for soda-typed saline-alkaline soil and itsmechanisms, mineral composition of soda-typed saline-alkaline soil and the practice ofaluminium sulfate used in field was simulated in this study. Aluminum sulfate was selected to bethe modifier for montmorillonite(Mt). Montmorillonite-hydroxyaluminumcomplexes (Mt-HyAl)were synthesized by adding aluminum sulfate solution with different OH/Al into Mt. Mt-HyAlwas used to adsorb humic acid (HA) and fulvic acid (FA). Then, batch experiments were carriedout to obtain the adsorption isotherm of the humic acid on Mt-HyAl. X-ray diffraction (XRD)and Infrared spectroscopy (IR) as the analysis methods were used to explore the adsorptionmechanisms of the humic acid on Mt-HyAl.Providing important theoretical basis for the rapidaccumulation of organic matter on soda salt-alkalinized soil and the construction of environmentfriendly technical system for soda salt-alkalinized soil development is the aim of this paper. Theresults of the study summarized as follows:1. The potentionmetric titration curve of aluminum sulfate showed that there was there bufferplatforms and two abrupt changes in titration curve. The range of the first buffer platform wasfrom0.175to2.367of OH/Al and from3.45to4.50of pH value of which polynuclear hydroxyaluminium ions were its dominant hydrolysate. The second buffer platform ranged from3.192to4.150of OH/Al and9.65to10.58of pH value, and its dominant hydrolysate was composed ofsol aluminum hydroxide and amorphous aluminium hydroxide. When OH/Al was above4.350and pH was greater than11.41the curve had the third buffer platform. The rise of the pH valueof the solution is similar to the first and second platforms and the its dominant hydrolysate wereAl(OH)－4、sol aluminum hydroxide and amorphous aluminium hydroxide. The OH/Al valuescale of two abrupt changes in titration curve was from2.367to3.192and from4.150to4.350,respectively. The pH value scale of two abrupt changes was from4.50to9.65and from10.58to11.41, respectively. The dominant hydrolysates of two abrupt change were respectivepolynuclear hydroxy aluminium ions、 sol aluminum hydroxide、 amorphous aluminiumhydroxide and sol aluminum hydroxide、 amorphous aluminium hydroxide、Al(OH)－4.2. In adsorption thermodynamics experiments, the adsorption data indicated that correlation coefficient R of the Langmuir、Freundlich Isothermal adsorption equations for adsorption ofhumic acid by Mt and Mt Complexes samples both reached significant level. For HA, thevalue of R of Langmuir and Freundlich were0.975±0.023and0.966±0.047respectively. For FA,the value of R of Langmuir and Freundlich were0.986±0.008and0.973±0.014respectively.Langmuir model provided better correlation of the equilibrium data than the Freundlich modeland its standard deviation was smaller. The value of the fitted thermodynamics parameters n、KF、qmaxand KLof Mt-HyAl(OH/Al=3.0)、Mt-HyAl(OH/Al=2.0)、Mt-HyAl(OH/Al=3.5)were both greaterthan Mt inordinately. It was found that adsorption intensity of Mt for humic acid were improvedsignificantly by HyAl solution of which OH/Al was2.0、3.0、3.5and then increase theadsorption sites of Mt for HA and FA after they interacted with Mt.3. XRD analysis results of Mt-HyAl showed that hydroxyaluminum were not interlayered in Mt.The reason was that solution concentration, chemical composition, titration rate, stirring speedand other factors may limit the Keggin ions generated. The existence of SO42-in the solutioncould be the main factors which restrain Keggin ions to generate. The Hydroxyaluminum ionswere analyzed to be fixed on the outside surface or edge of Mt. SEM analysis showed that theHyAl solution increased the surface roughness of Mt-HyAl, which favored for humic acidadsorption. XRD and IR analysis results of Mt-HyAl-HA and Mt-HyAl-FA showed that humicacids were not interlayered in Mt-HyAl complexes. In the presence of hydroxylaluminium, HA、FA were not interlayered in Mt so hydroxylaluminium were demonstrated to play a vital role inthe formation of organo-mineral complexes.4. Aluminium sulphate hydrolysis products hydroxy aluminium ions、sol aluminum hydroxide、amorphous aluminium hydroxide could be fixed on the outside surface or edge of Mt. Theyplayed a vital role as a bridge to adsorpte humic acid through cation bridges、hydrogenbond(water bridges) and hydroxide bridges. In addition, aluminum sulfate is a kind of flocculant.In the process of aluminum hydroxide precipitation formation, humic acid could be adhesived、furled and captured into the precipitation concurrently and were peridiumed on the surface of Mtfinally and then accelerate the adsorption of Mt for HA and FA. |
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