Inhibiting water evaporation of sand soil with clay modified by linear alklybezene sulfonates

Abstract: Desertification is one of the most serious environment problems in the world. Three methods commonly used in desertification control are engineering, chemical and biological sand fixation. Aiming at available water conservation in desertification ecological restoration, the clay-based modified materials were prepared by clay and sodium dodecyl benzene sulphonate (LAS) composite. LAS (2, 4, 6 and 8 g) was individually dissolved into 15 g distilled water while strong stirring for 10 minutes. Then, 3 g bentonite was slowly added into the solutions under strong stirring. The slurry was sprinkled onto sand with a relative humidity of 40%. The samples were regarded as L1, L2, L3 and L4, respectively according to the different contents of LAS (2, 4, 6 and 8 g), and the original clay L was as control group. The water retention property was studied in simulated desertification climate and the materials were analyzed and characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD) and thermal gravity analysis (TGA). The materials were placed at 30 cm blow the 500 W ultraviolet (UV) carbon arc lamp to test the resistance to aging. The results showed that the water content of the control group fell sharply to zero just in 3 days. The falling rates of the water content for all the modified materials slowed down, and the water retention property was improved with increasing LAS content. L4 had the best performance for moisture content of 3.2% on the tenth day. It was because the clay particles had been cemented into large particles by LAS and the hydrophobic ends of LAS were connected to form a hydrophobic network that can inhibit water evaporation. As such, samples with high LAS content had better water retention ability. The aging results showed that the compression strength were all higher than 4.25 MPa. Samples with high LAS content had higher strength and the compression strength of L4 was 6.35 MPa. The compression strength and mass lost was small after aging and highest in samples with high LAS content. After 300 hours aging, the lost of L4 was highest with the strength loss rate of 8.7% and mass loss of 1.7%. It was because the photolysis rate of LAS in solid-state was very low and its decomposition temperature was above 450℃. So the materials had good performance of resistance to aging. The SEM images showed that the original clay particles were small and loosely arranged. There were abundant channels of different pore size to transport water. The clay particles in the modified materials were cemented by LAS so that some water conducting channels were cut off. At the same time, the interaction of hydrophobic ends of LAS made more clay pores changing from hydrophilic to hydrophobic state. Then it was more difficult for water to rise and so the water retention property was enhanced. The FTIR figure showed that the infrared absorption characteristic peaks of original clay also existed in the modified clay, which indicated that the phase composition of clay did not change. The XRD figure showed that d001 interlamellar crystal spacing was 1.40643 nm for original clay, and 1.42420 nm for the modified clay. And there was almost no change in the interlamellar crystal spacing, which indicated that the modification didn't change the layered microstructure. The TG and DSC curves showed that the original clay kept losing water over temperature and most of the free water and interlayer adsorbed water escaped at and below 200℃. By comparison, there was almost no moisture loss of modified clay below 200℃. It was because the interaction between hydrophilic ends of LAS and the free water and adsorbed water made the water more stable. Grass-planting experiment showed that reasonable mass ratio of LAS and clay was 2:1. The materials not only had good water retention property but also maintained sound air permeability so the germination rate of grass seed significantly increased from 8% to 43%. After that, more LAS would block a part of the clay pores, which would influence the air permeability and thereby decrease the germination rate.