Abstract
Among the existing methods for removing the phosphates from water, the most effective and cheap is the method of ion exchange. The advantage of this method is the possibility to process regeneration solutions with obtaining the liquid fertilizers or other useful products. The processes of sorption of phosphates on the weak-base and strong-base anionites are investigated. We examined the dynamics of sorption of phosphates from the model solutions in the distilled and tap water depending on the form of ionite. The influence is established of the competing compounds of sulphates and chlorides in tap water on the effectiveness of removal of phosphate-anions. We explored the processes of regeneration of strong-base anionite in the phosphate and phosphate-sulfate form. The regeneration of anionite in the phosphate form was carried out with the 10 and 15 % solutions of sodium chloride and the 10 % solution of ammonium chloride. In order to regenerate anionite in the sulphate-phosphate form, the solutions of sodium chloride were used at concentration 10 %. The regeneration solutions contained sodium phosphate or ammonium phosphate, sodium phosphate-sulphate, respectively. We established that the effective sedimentation of phosphates occurs at molar ratio (NH 4 ) 3 PO 4 and MgCl 2 1:1, at optimum value pH=9. The optimal dosage of magnesium chloride and the value of pH are determined. This will provide 99.99 % sedimentation of phosphates from the regeneration solutions in the form of insoluble sediment. We proposed a method for removal from the regeneration solutions of the interfering compounds of sulphates in the form of gypsum, which will make it possible to repeatedly use these solutions for the regeneration of anionite. The essence of this method is the addition of chloride calcium to the solution, resulting in gypsum falling out into the sediment. The excess of calcium is removed in the form of calcium carbonate when soda is added.
Highlights
Phosphorus belongs to the biogenic elements and is essential for the growth of organisms
Despite the fact that phosphorus compounds play a decisive role in the processes of photosynthesis and life of living organisms, their excess in the aquatic environment under certain temperatures leads to eutrophication
It is shown that the exchange capacity of the anionite Dowex Marathon WBA on phosphates is low and its use for the removal of phosphates is not advisable
Summary
Phosphorus belongs to the biogenic elements and is essential for the growth of organisms This is a nutrient resource that determines the productivity of autotrophs of various environmental systems and primary productivity of water reservoirs. The main sources of inflow of phosphorus to the water areas of the European Union are fertilizers – 16 %, industry – 7 %, background sources – 9 %, human and domestic waste – 24 %, detergents – 10 %, wastewater – 34 % [1,2,3]. That is why it is a relevant issue to purify the wastewater from phosphates, as well as solving the problem on selecting the best method of purification. This method should provide effective and low-waste removal of phosphate-ions from water
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