Preparation Of Goethite With High Specific Surface And Its Adsorption Characteristics For Fluorine

The fluorine-containing wastewater in the field of nonferrous metallurgy has a wide range of sources and complex components.The depth and efficient removal of fluorine from wastewater are common problems many metallurgical enterprises face in China.The adsorption method is widely used in treating hydrometallurgical fluoride-containing wastewater owing to its simplicity in operation and pollution-free.However,some problems such as low adsorption capacity,long treatment cycle,the high price of adsorbent,and rapid attenuation of its performance have been existing.The development of an efficient and economical fluorine adsorbent material is an urgent bottleneck in fluorine removal from hydrometallurgical wastewater.Aiming at the typical fluorine-containing wastewater in the field of hydrometallurgy,a high specific surface goethite adsorbent with a large specific surface area,strong fluorine adsorption capacity,and good reusability was prepared.The adsorption effect and mechanism of the adsorbent on F^-were investigated.The main research contents and results are as follows:（1）The goethite adsorbent material with a high specific surface was prepared by the shearing-enhanced method,and modern characterization methods analyzed its microstructure and physicochemical properties.The results show that the goethite has low crystallinity,small particle size,uniform dispersion,and typical needle-like morphology.Under the optimal condition of a Fe³⁺mass concentration of 15 g/L,a temperature of 80℃,a solution pH of 3.0,a reaction time of 1.5 h,a shearing speed of 6000 rpm,and a PVP concentration of 0.2 g/L,the specific surface area of goethite is206.91 m²/g,with internal mesoporous structure,and the pH_IEPof goethite surface is 8.35.（2）Taking NaF simulated solution as the research target,the single-factor experiment was used to investigate the influences of various factors on fluoride adsorption by the goethite.The result showed that the adsorption rate and adsorption capacity were 92.2%and 9.22 mg/g,respectively,under the condition of an initial solution pH of 4,a reaction time of 2 h,a reaction temperature of 25℃,a fluorine concentration of100 mg/L,and a goethite dosage of 10 g/L.The presence of Cl^-and NO₃^-in the solution has less impact on fluorine adsorption,while SO₄^2-can significantly affect the adsorption of fluoride through competitive action.On this basis,the adsorption applicability of high specific surface goethite to the defluorination alkali washing solution of zinc oxide dust in zinc hydrometallurgy was verified.After two adsorption treatments,the concentration of fluorine in the solution decreased from 203.56 mg/L to2.35 mg/L.In addition,the desorption experiment,which uses NaOH as the desorption agent,showed that the desorption rate of goethite reached94.88%at a pH of 14.（3）The thermodynamics of F^-adsorption of goethite with a high specific surface area was studied.The result showed that the fluorine adsorption isotherm of goethite follows the Langmuir model.According to the model,the maximum adsorption capacity of goethite for F^-is 43.01mg/g.The fluoride adsorption of goethite was a spontaneous（ΔG^θ<0）,endothermic（ΔH^θ>0）,and entropy increased（ΔS^θ>0）process.The increasing temperature was favorable for adsorption,but the adsorption process was less affected by temperature.（4）The kinetic studies of the adsorption process showed that the fluoride adsorption of goethite at different temperatures,initial pH,and initial F^-concentration conform to the characteristics of the pseudo-second-order kinetic model,and its rate-limiting step was chemical reactions related to the characteristic surface adsorption of goethite,and the apparent activation energy of the adsorption reaction was 15.14 kJ/mol,and the frequency factor was 28.22.