Experimental Study On Treating Rare Earth Sodium Saponification Wastewater

Rare earth factory in Inner Mongolia Baotou use sodium saponification system of P507+NaOH+kerosene+HCl to separate rare earth minerals, producing the rare earth sodiumsaponification wastewater is acid, turbid, high hardness, high concentrations of sodiumchloride and have ammonia nitrogen, oils and other pollutants. In order to reduce theenvironmental pollution and waste of resources, this paper selects the bipolar membraneelectrodialysis treat the rare earth sodium saponification wastewater, turning the sodiumchloride in the waste water into sodium hydroxide and hydrochloric acid reuse, meanwhilemake the quality indicators of treated waste water can reachof the water quality indexof industrial recycling cooling water. But because of bipolar membrane electrodialysis hascertain requirements on water quality, so it must be pretreated to the raw water. Throughanalysizing the pollution situation of raw water, the paper selects pretreatment process ofthe caustic soda-soda chemical softening and modified zeolite/activated carbon removingoil to treat the rare earth sodium saponification waste water, making hardness, oil, CODand turbidity in the wastewater are significantly reduced, reaching into the membranerequirements of bipolar membrane electrodialysis.In experiment of caustic soda-soda chemical softening treat hardness, through singlefactor and orthogonal experiments to study the effect of Na2CO3dosage, NaOHdosage, stirring time and settling time on the hardness softening efficiency, and reachthe best processing condition: the Na2CO3dosage is0.65g/L, the NaOH dosage is1.1g/L,precipitation time is40min, stirring time is20min. Under this condition, hardnessefficiency of rare earth sodium saponification waste reach92.6%, total hardness in wastewater decrease from935mg/L to69.2mg/L.In the modified zeolite and activated carbon from coconut shell oil removalexperiment, study HDTMA modifier concentration, modification time, modified zeoliteand activated carbon dosage, adsorption time, pH and adsorption temperature have effecton oil removal efficiency, thus reach the optimum conditions. Under the optimal conditions, the modified zeolite on oil removal rate reach81.6%, and removal oil rate of activatedcarbon is94.2%, combined treatment make oil concentration drop to0.137mg/L is lessthan1mg/L, reached into the membrane requirements of bipolar membrane electrodialysis.At the same time, the treated wastewater is not noscaling tendency on the membranesurface by scaling prediction, which provides a guarantee for the stable operation ofbipolar membrane electrodialysis.In the experiment of treating wastewater with a three compartment bipolar membraneelectrodialysis, studying effect of initial acid and base concentration and current on stackvoltage, acid-base production, current efficiency and energy consumption, thus determinethe optimum conditions: the current is25A, the initial acid and base concentration is0.3mol/L. Then under this condition, the reaction time prolong to5h to study dealing withthe situation of the rare earth sodium saponification wastewater, the experimental resultsshow that: the NaCl concentration drop to893mg/L from118g/L directly, standard of waterquality indexes of the treated wastewater can fully meet the industrial circulating coolingwater, meanwhile the concentration of recuperated sodium hydroxide and hydrochloricacid reach2.12mol/L and1.78mol/L respectively.