Study On The Preparation Of Medium Element Water-soluble Fertilizer From Fluorinated Wastewater

In this paper,calcium nitrate precipitation was used to remove fluorine from fluorine-containing wastewater,and the medium element water-soluble fertilizer with nitrogen-containing potassium was prepared by using the filtrate after fluoride removal.the most suitable technological conditions and seed soaking concentration were obtained.Using calcium nitrate with high solubility of calcium and nitrogen as precipitator to remove fluoride ion in wastewater,the pH value of wastewater was adjusted by potassium hydroxide.The optimum conditions were as follows:pH=13±0.5,The amount of calcium nitrate added is satisfied n(Ca²⁺):n（F^-）=0.6,stirring 60 min,standing 60 min,fluoride removal 99.987%,fluoride concentration less than 10 mg/L.in solution after fluoride removalThe solubility of calcium nitrate and magnesium nitrate in the filtrate after fluoride removal was studied by isothermal equilibrium dissolution according to the principle of phase equilibrium of water salt system.the phase diagram of water salt system of Ca（NO₃）₂-Mg（NO₃）₂-fluoride removal filtrate system at 0℃,15℃,25℃,pH=3,4 and 5was drawn.The formula area and stability of liquid-type medium-element water-soluble fertilizer were analyzed according to the phase diagram.The medium-element water-soluble fertilizer with different formula and total nutrient content met the requirements of Ca+Mg≥100g/L,N+K₂O≥260g/L was prepared.The technical index was better than the agricultural standard（NY2266-2010）.Containment targets for mercury,arsenic,cadmium,lead and chromium meet NY 1110-2006 requirements.The soaking conditions and effects of water-soluble fertilizer with medium element in four formulations were investigated.The results showed that the four kinds of water-soluble fertilizers with medium element could significantly increase the germination rate,germination potential,seedling length,root fresh weight,POD enzyme and CAT enzyme activity of wheat,leek,corn and rice in a certain concentration range.Through the analysis of the test results,the formula of water-soluble fertilizer and the method of seed soaking were selected.