CALCULATION OF A MULTI-CHAMBER FLOTATOR FOR CLEANING WASTEWATER FROM HEAVY METALS

Abstract

To date, the treatment of industrial wastewater from heavy metals is carried out mainly using reagent technologies. Heavy metals are separated in the form of insoluble compounds: hydroxides, sulphides, carbonates. Usually, phase separation occurs as a result of sedimentation. A more efficient method of separation is reagent flotation. In this case metals are separated in the form of flotation sludge on the water surface. Flotation separation of metal hydroxides allows to obtain a sludge with moisture content of 92–94%, while in sedimentation the moisture content of the sludge is 99%. As a consequence the amount of solid phase released is reduced and the material intensity of the equipment is significantly decreases. However, when wastewater contains metals with different pH values of hydroxide formation, it is difficult to ensure the required quality of treated water. At treatment plants, a compromise pH value is set, which is not always optimal for all metals. As a consequence, there is incomplete precipitation of some metals that have a pH of hydroxide formation different from the compromise value of pH alkalisation of wastewater. For completeness of metal precipitation it is more effective to carry out the process of alkalinisation in stages, alternating between wastewater alkalinisation and subsequent separation of formed metal hydroxides. To realise this process, multi-chamber flotation plants with built-in mixers and crystallisers have been developed. In a multi-chamber flotation cell, each flotation module can be set to its own conditions for efficient metal recovery by adjusting the optimum pH value for a certain metal. The technological scheme of wastewater treatment with heavy metals using multi-compartment flotation modules, which can be arranged both in series and in parallel, is proposed. The description of the research methodology is given, as well as the scheme of the experimental unit. The method of calculation of multi-chamber flotators is described, allowing on the basis of the obtained experimental data to determine  the structural dimensions of all the constituent modules of the water treatment plant: flotation cells, mixer, crystalliser. The dependence for determining the height of the flotation sludge layer is proposed. As an example, the calculation of the first flotation module of a multi-compartment flotator with sequential placement of modules is given.