Study On The Characteristic And Mechanism Of Fe-oxides Cemented With Clays

Fe,Al oxides and kaolinite are the main and active constitutes of red soil in the south of China.The interaction between them is very important for the forming of soil aggregate,protecting of soil quality,clarifying the quality of rock and soil mechanics.According to the forms of Fe oxides that occur in the actual soil, we synthesized crystalloid .amorphous and Fe oxides - kaolinite associations, using XRD,SEM/EDS,IR and other method to analyze the crystal, figure and chemical bond. Studied the interaction process of the Fe oxides - kaolinite associations system, discussed the essence of this interaction. The main results were as follows:1. The coating interaction, between goethite, hematite- kaolinite by mechanical mix.(1) The XRD patterns showed that the extra peaks of kaolinite in the associations becoming weak, and some peaks disappeared. It was indicated that the products may have coated with Fe oxides or covered with them.(2) The SEM micrographs and EDS of associations indicated that the products coated with Fe oxides, and the Fe oxides distributed equably, but the content of Fe is low, so the effect of coat is not distinct. (3) By FT-IR spectroscopy, it could be deduced that the main reaction between Fe oxides and kaolinite was between Si-O bond and Fe-O bond, H-bond was proposed to be formed between Si-OH and Fe-OH,they connected by chemical bond.Goethite and hematite all can connected with kaolinite by chemical bond,but the coat effect are not distinct, the hematite- kaolinite coat interaction was better than goethite.2. The transforming characteristic of amorphous Fe oxides- kaolinite to crystalline -kaolinite. (1) Influencing of aging time in the intermediate phases from amorphous to crystalline. The XRD patterns showed that the extra peaks of kaolinite in the associations becoming weaker, and some peaks disappeared along with the aging time.EDS indicated that the Fe content in the associations was becoming higher with the aging time prolong, but Fe content of up solution was becoming lower contrarily.This indicated that the amorphous Fe oxides transformed to crystalline and coated with kaolinite completely with the aging time prolong. (2) aging temperature had no influence to the coat interaction , which because the aging temperature (25℃,40℃,60℃)had no big difference in the laboratory.(3) By FT-IR spectroscopy, it could be deduced that the chemical environment of Si-O bond of kaolinite was changed, which cementated with the Fe-O bond of ferrihydrite. They connected by chemical bond, and the coating effect was better than the mechanical mix.3.The transforming characteristic of different Fe salt (Fe²⁺,Fe³⁺)- kaolinite.(1)The influencing of aging time and temperature in the intermediate phases from amorphous to crystalline. XRD,SEM/ EDS indicated that the crystalline Fe oxides was becoming more and content of Fe in the associations was becoming higher with the aging time prolong, Which indicated that the amorphous Fe oxides transformed to crystalline and coated with kaolinite completely with the aging time prolong. aging temperature had no influence to the coat interaction , which because the aging temperature (25℃,40℃,60℃)had no big difference in the laboratory. (2) XRD,SEM/ EDS,IR indicated that Fe oxides coated with kaolinite during the process of transforming from amorphous to crystalline, they connected by chemical bond, thecoating effect of Fe³⁺- kaolinite was better than the Fe²⁺ - kaolinite .4. The studying of specific surface area (SSA) and pore diameter. The specific surface area (SSA) of the amorphous ferrihydrite was the highest (256.8m²/g), then was crystal hematite (103.1m²/g), kaolinite (28.6m²/g). The SSA of the crystal hematite -kaolinite associations was 72.1 m²/g, which was higher then the Fe³⁺ and Fe²⁺ oxides-kaolinite associations.the SSA of Fe³⁺ oxides-kaolinite associations was 38.2 m²/g, Fe²⁺ oxides-kaolinite associations was 35.3 m²/g. the SSA of each kind of associations was higher then kaolinite.But whatever associations or monomers, the highest pore diameter were all 0.4nm-0.6nm, have no distinct change. Compared to the kaolinite, all the pore volume of associations was small.