| Mineral mining and ore washing process produce a large quantity of mineral water with much sludge which is difficult to settle. Although the sludge in different types of waste water is complicated, among its mineral composition, clay mineral is considered to be the biggest influence on the treatment of high-sludge waste water, and makes the process complicated and difficult to achieve dehydration and settlement. Following are some examples:drilling mud in oil industry, the coal slime water, the oil sands tailings water separation process of clay and bauxite tailings produced in the process of mining, etc.,_all of them have problems such as high content of clay mineral, large quantity and high cost for treatment, if not be properly handled, it will lead to serious environmental problems.In addition, studies have proved that polarity component exists on the surface of calcium sulfate combined with water, which can affect the interface reaction process in the multiphase system. This paper aims at explaining the cause of the settlement of clay minerals in the waste water with calcium sulphate dihydrate and also by calculating and studying the microcosmic effect of potential energy of clay minerals in the water.The main contents of the study as follows:(1) The effect of addition of calcium sulphate dehydrate, solution pH and Sodium solution ionic strength on settlement of clay minerals is investigated. As the addition of calcium sulphate dihydrate increases, the settlement speed of the clay minerals accelerates first, then slow down. As solution pH grows or Sodium solution ionic strength reduces, the settlement of the clay minerals without calcium sulphate dehydrate in clay suspensions shows a quick slowing trend. But when calcium sulphate dehydrate is added, particles in the solutions get easy to agglomerate and settle down. Solution pH or Sodium solution ionic strength almost has no effect on the settlement of the clay minerals with calcium sulphate dehydrate in clay suspensions.(2) The experimental results are analyzed by Zeta potential of clay minerals and the extended DLVO theory. As the addition of calcium sulphate dihydrate or solution pH reduced or the strength of the sodium ions increased, the negative charge of both kaolinite and montmorillonite on particles surface reduces, with which the total surface potential energy between particles also reduce. Additionally, solution pH and sodium ionic strength has no effect on the Zeta potential of clay minerals after calcium sulphate dehydrate is added. Meanwhile the surface Zeta potential of calcium sulphate dihydrate is positive and the total potential energy is always negative. There is no energy barrier which can be seen as mutual adsorption condensation. So the addition of dihydrate calcium sulphate is not only reduce the repulsion between the clay mineral particles, but also promote the settlement of the clay minerals by agglomerating with clay minerals.(3) The sedimentation of coal slurry (slime water) was accelerated by using desulfurization gypsum solid waste. Thereby the effect of wastewater purification can be enhanced. The rules of sedimentation process between desulfurization gypsum and coal slurry containing fine coal and kaolinite was examined and analysed by the method of turbidimetry. The results indicated that desulfurization gypsum caused no effect on the sedimentation of fine coal, but had evidently positive effects on that of kaolinite. Mixed with desulfurization gypsum, the turbidity value of coal slurry containing kaolinite dropped to 131 NTU from 239 NTU.The settlement of desulfurization gypsum and coal slime water mainly because of the effects of calcium sulfate hemihydrate and the coal slime water. |
PDF Full Text Request