Ryabchevsky O. The treatment of waste water for chromium and nickel ions removal by clay sorbents.

PhD Thesis for the degree of the candidate of Engineering sciences in the specialty 21.06.01 - Environmental safety. – National Aviation University, Kyiv, 2019. The thesis is aimed at solving the topical scientific and applied task of improving the level of environmental safety of the industrial waste water treatment from chromium (III) and nickel (II) ions using natural clay sorbents. The structure and chemical composition of clay sorbents have been investigated by X-ray analysis, gas adsorption and gravimetric method. The sorption properties of natural clay materials (spondyl green clay and dark brown loam) have been studied for chromium (III) and nickel (II) ions, the main parameters of the adsorption process and the maximum efficiency of the sorbents application have been determined. It has been established that in order to achieve the maximum level of pollutants removal with minimum consumption of sorption material, the ratio of “solid matter – liquid” should be 1:50. The sorption data has been arranged into sorption models and the models that best describe the process are selected. It has been found that complete adsorption capacity of the sample on the spondyl green clay ions Ni2+ is 1.5 times higher than the standard dark brown loam and it reaches 0.245 mg/g. The adsorption capacity of spondyl green clay in relation to ions of Cr3+ is 0,042 mg/g, and when applying DBL - sorption is not observed. New sorption clay materials have been obtained on the basis of natural samples by their chemical modification in order to improve the sorption properties. The basic conditions of the modification process and the growth of the maximum sorption capacity are also determined. The ecological risk assessment of the clay sorbents application in water treatment from metal ions is based on the results of biotesting with the help of test objects Allium cepa L. and lactuca sativa L. The method of correlation-regression analysis has demonstrated the close dependence between the change in the relative ecological risk and waste water treatment with spondyl green clay and of dark brown loam, which is seen from the changes in the indicative parameters of the test objects Allium cepa L. and Lactuca sativa L. The calculated correlation coefficients indicate a strong correlation in the application of Lactuca sativa L. and the sufficient correlation for the Allium cepa L. The method of the worked sorbents management through their deposit in constructional mixtures based on cement has been explored and discussed; it allows reducing the amount of sludge and provides reliable fixation of sorbate, preventing the migration of heavy metals in the water-soil system, including changes in ambient pH and temperature. Key words: environmental safety, sorption, treatment of waste water, chromium (III) and nickel (II) ions, modified clay sorbents, ecological risk.