Improving the efficiency of using sands as artificial geochemical barriers

The interaction of sands as artificial geochemical barriers with nickel chloride solutions simulating technological effluents is investigated. The effect of pre-acid treatment of sands on their ability to absorb nickel (II) ions is considered experimentally. In experiments, sands with different quartz contents have been studied, in which the only impurity element was aluminum oxide in an amount from 1 to 10% (wt.). Pretreatment of sands with 0.1 M hydrochloric acid solution has been carried out for 0.5 hours by stirring a water-sand suspension on a magnetic stirrer. Traditional methods of colloidal chemical research have been used. Under static conditions, a flask with a sand suspension (3 g) and a solution has been placed in a special shaker, under dynamic conditions, a solution has been passed through a layer of sand (3 g) in a column. The nickel (II) content in the solutions has been determined by photometric method with dimethylglyoxime. According to the results of adsorption studies, an increase in the maximum adsorption values from 15–20 to 50–56% has been achieved, depending on the type of sand and the quartz content in it. When filtering solutions through a layer of sand, the degree of retention of nickel (II) ions on the activated surface of the grains increases. At a filtration rate of 1×10-3 dm3/min and the same filling height (2.7 ± 0.1 cm), the efficiency of removing nickel ions from the solution increases. At the same time, an increase in efficiency by 1–1.5% is typical for sands with high natural indicators of 95–98%. On sands, the natural capacity of which initially does not exceed 65–70%, the increase in efficiency is more significant and amounts to 5% or more. In general, the increase in efficiency is proportional to the quartz content, i.e., the treatment of sand grains with hydrochloric acid activates mainly those areas of the surface on which silicon bonds are localized, i.e. siloxane and silanol groupings, which act as adsorption centers.