A single-factor experiment of copper ion adsorption on pure palygorskite was carried out to understand the Cu2+ sorption of palygorskite—an important clay mineral in soil and sedimentary rock. In addition, pH of the solution and the surface microstructure of palygorskite were investigated before and after adsorption. The experimental results indicated that efficiency of Cu2+ removal was related to the oscillation rate of the specimen shaker, sorption time, initial pH value and the amount of adsorbent added. Palygorskite induced Cu2+ hydrolysis and interaction between copper hydroxide colloids and palygorskite surfaces, as observed with transmission electron microscopy (TEM), were the main contributions to palygorskite removal of Cu2+. This mechanism was different from adsorption at the mineral-water interface. It was proposed that surface hydrolysis of palygorskite raised the alkalinity of the palygorskite-water interface and suspension system. Thus, the induced pH of the solution was then high enough for Cu2+ hydrolysis on the mineral surface and in solution.
Palygorskite clays sampled from palygorskite clay deposits in Jiangsu and Anhui provinces were investigated by transmission electron microscopy (TEM). Many intergrowth phenomena of special ultra-microstructure between smectite and palygorskite were found. The ultra-microstructure indicates that palygorsite fiberrous crystals grow along (001) of primary smectite through structural transformation and decomposition of the primary smectite. According to field investigation and X-ray diffraction (XRD) analyses, the transformation mechanism and process can be described as: formation of smectite from basalt weathering deposited in localiza- tion basin; evaporation of lake water in aridity environment causing pH increase and concentra- tion of magnesium ion in interstice water of sediment smectite in the lake basin. Under alkaline conditions, magnesium ion occupied interlayer positions of the smectite. Because of the misfit between magnesium octahedral sheet and smectite layer, magnesium ion interaction with smec- tite layers caused the smectite to transform into palygorskite, and resulted in the formation of smectite and palygorskite complex particulates, and even smaller secondary smectite crystal plates. The transformation of smectite structure resulted in the formation of nanometer minerals with large specific surface area and excellent property of physics and chemistry in smec- tite-palygorskite mixing clay. The results from TEM investigation are important for understanding properties of palygorskite clay and application.
CHEN Tianhu1,,XU Huifang2,LU Anhuai3,XU Xiaochun1,PENG Shuchuan1 2 &YUE Shucang1 1.College of Resources and Environmental Engineering,Hefei University of Technology,Hefei 230009,China
