Wet-process Phosphoric Acid Defluorination Purification Studies

Phosphoric acid as one of important intermidiate in chemical engineeringindustry,which can be used in production of phosphorus ammonium, doublesuperphosphate,compound fertilizer, and other different kinds of phosphate.Phosphoric acid can also be used in the electron, medicine, foodstuff industry, and soon.Phosphoric acid is one of indispensable raw material in these industry. End use ofphosohoric acid depends on its degree of purification ,whereas its purity generaldepends on its production method and its degree of purification. So many people payclose attention to phosphoric acid purification。Chemical precipitation-solvent precipitation process was adopted, hopingcontent of F^- in the phosphoric acid can be descended to a feasible level, acquiringbetter defluorination ratio. The thesis includes four parts:Pretreatment of raw acid: aging-defecation, experiments of decolour anddesulfuration. After pretreatment, some impurities contents are lower, and phosphoricacid light transmittance was from 29.5％mount up to 85.7％,the content of SO₄^2- wasfrom 3.71％(w％) drop to 0.0369％(w％), the rate of desulphurization was 99.0％Chemical precipitation process: using sodium carbonate as defluorinationsubstance. The experimentation conditions were obtained: the way of sodiumcarbonate joined, rate of agitation, healing time, reaction time, dosage ofdefluorination substance, reaction time and reaction temperature were furtheroptimized. Acquiring suitable reaction conditions: sodium carbonate was joined instate of solid, rate of agitation was 300rpm, healing time was two hours,defluorination substance dosage was 25％(w％) more than theory quantity, reactiontime was two hours, reaction temperature was 30℃。After chemical precipitation,therate of defluorination was 68.60％(w％), the recovery rate of P₂O₅ was 92.8％(w％)。Aid-defluorination substances were also researched, choosing two kinds ofaid-defluorination substances: silica and alumina cream. Dosage of silica and aluminacream were further optimized. The suitable experimentation conditions were acquired: acquiring suitable reactive conditions: SiO₂/H₃PO₄(raw phosphoric aid)was0.11%(w%), Al(OH)₃/H₃PO₄(raw phosphoric aid)was 0.06%(W%)..Reaction kinetics of sodium carbonate and silicofluoric acid was also researched,reaction kinetics model was acquired. The result proved that the reaction wassecond-order reaction, relationship of reaction rate constant of K and reactiontemperature T was: k=14.67 exp(27.41×10³/RT).Solvent precipitation process: choosing ethanol as organic solvent, RNH₂ asaccessory ingredient, and phosphoric acid purified by chemical precipitation methodwas named as first purified phosphoric aid. The suitable experimentation conditionswere acquired: the volume of ethanol to phosphoric acid was 2:1, RNH₂/H₃PO₄(purified phosphoric aid) was 3.24%(w%), reaction time was 90min, reactiontemperature was 45℃, it took 45min for ethanol to instill into reactor. Afterchemical-solvent precipitation, the rate of defluorination was 96.44%(w%), recoveryrate of P₂O₅ was 86.1%(w%).