【作者】 姜科；

【导师】 周康根；

【作者基本信息】 中南大学 ， 冶金工程， 2014， 博士

【摘要】 摘要：我国是世界上最大的氟化盐生产国,氟化盐生产过程产生的大量高浓度含氟废水,对动植物和人体造成了严重的危害。目前,含氟废水主要采用传统的化学沉淀法处理,但沉淀过程产生的污泥含水率高、回收价值低、处理处置困难。与此同时,作为宝贵的非金属矿产品,萤石资源面临严重的紧缺危机。从资源循环和可持续发展的角度考虑,实现含氟废水中氟的回收具有重要的经济和环境意义。本论文以湖南某氟化盐公司工业含氟废水为研究对象,以实现废水中氟的资源化及出水达标排放为目标,提出了采用晶种诱导结晶法从废水中分步回收砂状冰晶石和砂状氟化钙的新思路,分别设计了新型沉淀反应与固液分离一体化装置和流化床结晶反应器,开展了砂状冰晶石结晶及砂状氟化钙结晶技术的系统研究,解决了传统工艺回收得到的冰晶石、氟化钙污泥含水率高、粒径小、不能回用的问题。主要研究结果如下：分别对冰晶石和氟化钙沉淀体系的固液平衡热力学进行了研究。(1)通过分析Al3+-Na+-F--H+-H2O体系中不同形态化合物的分布以及Na3AlF6、NaAlF4、Al(OH)3等固相稳定存在的条件,得出体系中稳定存在的固相应为Na3AlF6与NaAlF4[或Al(OH)3]的混合物,不能从废水中直接沉淀得到Na/Al分子比为3的冰晶石产品；溶液平衡总氟浓度越大,越有利于Na3AlF6的析出,有利于提高冰晶石Na/Al分子比。(2)通过分析Ca2+-F--H+-Al3+-H2O体系中CaF2沉淀溶解度与粒径的关系以及CaF2沉淀的介稳区,得出CaF2粒径越大,其活度积常数越小,溶解度越小,平衡总氟浓度越低,增大CaF2沉淀粒径是提高含氟废水处理效果的有效途径。氟化钙的溶解度曲线和过饱和溶解度曲线将溶液分成了不饱和区、介稳区和浑浊区,介稳区图可以对不同pH、不同Ca/F下氟化钙的成核过程进行预测。分别对砂状冰晶石和砂状氟化钙的回收工艺条件进行了研究。(1)研究了影响冰晶石砂状化及分子比的因素,得出延长晶种停留时间可以提高促进冰晶石沉淀砂状化,降低其含水率；提高沉淀剂铝酸钠溶液的Na/Al苛性比,可以将冰晶石分子比控制在2.4-3.O。(2)在流化床中开展了石英砂流态化实验,得出石英砂粒径越大,对应的流态化速度和带出速度都越大,有利于流化床操作流量的控制；流化床的床层压差可以作为控制流化床运行状态和排晶条件的重要指标。(3)研究了高过饱和度下流化床中氟化钙的结晶动力学,确定了氟化钙生长速率的动力学方程,得出在高过饱和度下,氟化钙颗粒与晶种之间通过吸附的方式团聚长大,并保持了较高的线性生长速率。(4)研究了高过饱和度下流化床中氟化钙的沉淀脱氟效果,以氢氧化钙悬浊液为沉淀剂对1000mg/L的HF废水进行了处理,控制废水流量为15L/h、Ca/F=1、pH=6.0-11.0时,出水总氟浓度为20-80mg/L。(5)研究了絮凝沉淀法处理低浓度含氟废水的工艺条件,控制反应pH=6.5-8.0、聚铝用量为100mg/L-400mg/L时,出水总氟浓度低于10mg/L。设计并使用诱导结晶反应器对氟化盐工业废水进行了分步回收和处理。(1)创新性设计了沉淀反应与固液分离一体化装置,采用该装置可以有效延长晶种停留时间,强化晶种诱导结晶过程。采用中试规模(处理能力80L/h)的沉淀反应与固液分离一体化装置对工业含氟废水进行了处理,控制反应pH=4.0-7.0、搅拌反应时间=14min、反应温度为35-50℃时,冰晶石产品回收率高于70%,冰晶石产品含水率低于20%、产品质量符合冰晶石国家标准(GB/T4291-2007)的要求。(2)设计并使用处理能力为0.49m3/h的流化床结晶反应器对总氟浓度为300-1000mg/L的工业综合废水进行了处理,以氢氧化钙悬浊液为沉淀剂,控制pH=7.0-10.0, Ca/F>1时,出水总氟浓度为15-40mg/L。流化床连续运行50h后,底部沉淀的平均粒径为159.0gm,含水率为27.0%,沉淀质量达到萤石粉矿质量要求(GB19321-88),可以在陶瓷、水泥等行业回用。(3)采用絮凝沉淀法对总氟浓度为20-40mg/L的氟化钙沉淀母液进行了深度处理,调节废水pH=7.0-8.0,控制聚铝投加量为200mg/L、废水流量为40L/h时,出水总氟浓度低于10mg/L,出水浊度低于30NTU,达到国家污水综合排放标准(GB8978-1996)的要求。在中试研究的基础上,以沉淀反应与固液分离一体化装置为核心设备,设计了处理能力为100m3/h的冰晶石回收系统。对单台处理能力为25m3/h的结晶反应器进行了工业化生产调试,从工业含氟废水中回收得到了质量合格(GB/T4291-2007)、粒径大的冰晶石产品,产品可作为铝电解行业原料回用。目前,冰晶石回收系统已成功实现工业化应用。更多还原

【Abstract】 Abstract:China is one of the largest producers of fluoride salts in the world. Large amount of high-concentration fluorine-containing wastewater are produced in fluorine industry, causing serious hazardous effects to the propagations and human-beings. The traditional methods for fluoride removal generally involve chemical precipitation and coagulation. The process generates large amounts of sludge with high water content, low quality, and non-reusability, which has to be disposed with increasing costs. Meanwhile, as precious non-metallic ore resources, fluorites are suffering a shortage crisis worldwide. Hence, the recovery of fluoride from industrial wastewater has great economic and environmental significance from the perspective of resource circulation and sustainable development.In this paper, the treatment of fluorine-containing industrial wastewater from a fluorine salts factory in Hunan Province has been investigated. The aim of the study is that the fluorine of wastewater can be recovered as resource, and that the effluent water quality can meet the discharge standard. A novel process, including recovery of sandy cryolite by crystallization and recovery of sandy calcium fluoride by crystallization, has been proposed. A noval reaction-separation integrated reactor and a fluidized bed reactor are designed, respectively. The crystallization technologies for recovery of sandy cryolite and sandy calcium fluoride are investigated. The problems that the cryoliye products and calcium fluoride products with small particle size and high water content cannot be reused have been solved by the novel process. The main results are as follows:The solid-liquid equilibrium conditions for the cryolite system and for the calcium fluoride system were investigated, respectively.(1) The distribution of dissolved Al and F complexes, and the stable zones of Na3AlF6, NaAlF4and A1(OH)3for Al3+-Na+-F--H+-H2O system were obtained. The results showed that the stable solids were Na3AlF6, NaAlF4or A1(OH)3, indicating that the cryolite with Na/Al molar ratio of3cannot be precipitated in wastewater. The solid of Na3AlF6with higher Na/Al molar ratio was favored to precipitate with increasing total concentration of fluoride.(2) The relationship between the solubility and particle size of calcium fluoride, and the metastable zones of calcium fluoride for Ca2+-F--H+-Al3+-H2O system were studied. The results showed that the solubility of CaF2and the equilibrium fluoride concentration decreased with increasing particle size of CaF2. The removal efficiency of fluoride increased with increasing particle size of calcium fluoride. The solubility curve and supersolubility curve divided the diagram into undersaturated region, metastable region, and labile region, respectively. The diagram of metastable region can be used to predict the nucleation process of calcium fluoride.The technological conditions for recovery of cryolite and recovery calcium fluoride were investigated, respectively.(1) The influence of several variables on the particle size and the molar ratio of cryolite products were studied. The results showed that the sandy cryolite products with low water content can be obtained with increasing seed retention time. The molar ratio of cryolite products can be maintained between2.4to3.0with increasing molar ratio of sodium aluminate.(2) The fluidized state of quartz sand in the fluidized bed (FBR) reactor was characterized. The results showed that the fluidization velocity and terminal velocity increased with increasing seed size, leading to a wide range of controlling conditions. The pressure difference can be used to predict the operation state and the particle size of pellets in the FBR.(3) The growth kinetics of calcium fluoride at high supersaturation was studied in the FBR, and the kinetics model of crystal growth was determined. The results showed that the calcium fluoride and fine particles grew in size with a high linear growth rate by adsorption and aggregation at high supersaturation.(4) The removal efficiency of fluoride by precipitation of calcium fluoride in the FBR was studied at high supersaturation. The synthetic HF wastewater was treated by the suspension of Ca(OH)2. The results showed that the fluoride concentration of the effluent was20to80mg/L at an influent flow of11to32L/h, an influent concentration of1000mg/L, Ca/F molar ratio above 1, and pH of6.0to11.0.(5) The deep removal efficiency of fluoride by flocculation was studied. The results showed that the fluoride concentration of the effluent was below10mg/L at a polyaluminium chloride dosage of100to400mg/L, and pH of6.5to8.0.Two crystallization reactors were designed and used for recovery and treatment of fluorine-containing industrial wastewater by steps.(1) A novel reaction-separation integrated reactor was designed. The seed retention time can be prolonged to strengthen the induced crystallization process in the integrated reactor. The fluorine-containing industrial wastewater was treated by a pilot-scale integrated reactor (capacity80L/h). The recovery rate of cryolite was above70%at a reaction temperature of35℃to50℃, a reaction pH of4.0to7.0, and a stirring reaction time of14min. The quality of cryolite products with large size and low water content (<20%) can meet the national standard of GB/T4291-2007.(2) The industrial complex wastewater with a fluoride concentration of300to1000mg/L was treated by a pilot-scale fluidized bed reactor (capacity0.49m3/h). The suspension of Ca(OH)2was used as the precipitant. The results showed that the fluoride concentration of the effluent was15to40mg/L at pH of7.0to10.0, and Ca/F molar ratio above1. After50h operation, the particle size and water content of calcium fluoride on bottom of the FBR were159.0μm and27.0%, respectively. The qualities of calcium fluoride products can meet the national standard of comminuted fluorspar (GB19321-88) in China. The calcium fluoride products could be used as raw materials in the ceramics and cement industry.(3) The mother liquor of calcium fluoride with a fluoride concentration of20to40mg/L was treated by flocculation process. The influent flow of the wastewater was40L/h, and the reaction pH of wastewater was adjusted at7.0to8.0. The dosage of polyaluminium chloride was200mg/L. The turbidity and fluoride concentration of effluent were less than30NTU and lOmg/L, respectively. The qualities of effluent can meet the national discharge standard (GB8978-1996).Based on the pilot-scale study, the system with a production capacity of100m3/h was designed for recovery of cryolite. The reaction-separation integrated reactor was the key equipment of the stystem. One of the integrated reactors with a production capacity of25m3/h was tested. The cryolite products with large size and high quality (GB/T4291-2007) can be precipitated from industrial wastewater. The system for recovery of cryolite has been successfully applied to industry.更多还原