Changing the permeability, mineral and soil structure of clay soil with chlorine dioxide

Vlok, Thomas Leslie Stewart (2020-03)

Thesis (MEng)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: Clay particles have small particle sizes. With the addition of water, the change in volume is greater in clay soils than coarse grained soils. When clay soils are mixed with a coarse-grained soil, the shrink and swell potential of the mixed soil will decrease. Chlorine dioxide is commonly used as a disinfectant or to control algae growth in sedimentation and flocculation basins. This chemical is used to kill bacteria in soil as well. Another use of chlorine dioxide is to increase the permeability of sandstone formations through the reaction of clays in these formations. The aim of this study is to determine if the increase in permeability as observed in the field can be replicated in the laboratory, by using the same concentration of chlorine dioxide that is used in agriculture to kill bacteria in the soil. The soil was treated with diluted chlorine dioxide to investigate the effect on the soil mineralogy and soil structure. Two different soils were used for these experiments. The first experiment was conducted with a clay soil. The second was a mixture of clay soil at the bottom with a coarse-grained soil on top to simulate different scenarios. Chlorine dioxide was mixed with water at different concentrations and introduced into the soil at a constant rate with a drip system. The chlorine dioxide is applied once then every third day for two weeks and then four litres of clean water was introduced into the soil with the same drip system. The soil was then dried and prepared for tests. X-Ray Fluorescence and X-Ray Diffraction was done on the soil to determine the mineralogy.A sieve analysis gave the particle size distribution for each sample. CT scan and scanning electron microscope tests were done to compare the soil structure before and after the experiment. A falling head permeability tests was also done on an untreated and treated sample to compare drainage of the soil. This study showed the mineralogy of the soil is not affected by chlorine dioxide. The CT scan showed the voids increase after the chlorine dioxide treatment. The scanning electron microscope showed the particles coalesced into flocculated layers, but the scans does not confirm the increase in void ratio from the CT scan. Particle size distribution does not show significant changes after the chlorine dioxide treatment. Chlorine dioxide treatment improved the drainage of the clay soil. Therefore, this treatment can be used to improve the permeability of clay soil.

AFRIKAANSE OPSOMMING: Geen opsomming

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