Tantalum and niobium leachate

A representative foreign company, the German firm H.C.Stark, reduces the consumption of chemical raw materials such as H2SO4 and the amount of slag by focusing on improving the internal circulation process in wet processes, and simultaneously recovers HF, NH3, and MIBK from various waste liquids. In the decomposition process, the use of H2SO4 is avoided, or the use of HF and H2SO4 is strictly controlled; the residues resulting from the decomposition are used to produce CaSO4 and CaF2 as other chemical raw materials, thereby reducing the amount of raw materials and residues generated. H.C.Stark Company also conducted research on a process that uses only one inorganic acid in the decomposition or extraction steps, and recovered HF from the residual liquid to use as a raw material for the decomposition process. The recovery of NH3 and MIBK is achieved through continuous evaporation using steam in a tower-type heat exchanger; by means of such recovery, the discharge of toxic and harmful wastewater can be significantly reduced (Zhang Xiangui, 1998; Zhou Hongxia, 1998).

The Conghua Smelting Plant (formerly Plant 723) uses a combined process to treat wastewater on-site, recovering ammonia (NH3) and fluorine (F) from the water, while simultaneously reducing the concentrations of fluoride (F-), sulfate (SO42-), and ammonium (NH4+) to levels below the **discharge standards. (1) Systematically study the characteristics of ammonia-nitrogen wastewater generated during the tantalum and niobium smelting process. A combined precipitation-desorption-biological treatment process is used to remove ammonia nitrogen from wastewater. Through ammonia nitrogen stripping tests, the effects of pH value, stripping temperature, and stripping time on the stripping efficiency were investigated ； Economically reasonable design parameters are determined based on the amount of alkali added and the stripping efficiency. (2) The alkali addition evaporation method is employed: lime (CaO) is used to convert ammonia from an ionic state to a free state, thereby separating it from water; after condensation and absorption, it is converted back into ammonia solution for reuse. Study the effects of holding time, holding temperature, solution concentration, and pH value on the efficiency of evaporative recovery of ammonia nitrogen ； On this basis, semi-industrial evaporation experiments were carried out to recover ammonia, in order to determine appropriate design parameters such as the amount of alkali added and the gas-liquid ratio. (3) Study the feasibility of using biological nitrification to treat ammonia-nitrogen wastewater resulting from evaporation and distillation, and propose a biological treatment process and design parameters suitable for ammonia-nitrogen in tantalum and niobium smelting wastewater. (4) Study the combined treatment of ammonia nitrogen wastewater from tantalum and niobium smelting using chemical precipitation and ion exchange methods. Through experiments with simulated wastewater and actual wastewater, the effects of factors such as pH value, reaction time t, dosage ratio, and influent concentration on the chemical reaction were studied to determine the optimal control conditions. Using zeolite as an ion exchanger, the effects of zeolite dosage M, reaction time t, pH value, reaction temperature T, and influent concentration c were studied. Factors affecting the efficiency of ion (zeolite) exchange method in treating low-concentration ammonia nitrogen wastewater and the influencing factors. A process combining chemical precipitation and ion exchange for the treatment of ammonia nitrogen wastewater from taantalum and niobium smelting in Conghua is proposed ； (5) Based on the above experimental data, a suitable treatment scheme for ammonia-nitrogen wastewater from tantalum and niobium smelting in Conghua is proposed, and the feasibility and technical-economic characteristics of this scheme are analyzed and compared.

Thank you for your answer. How can CaSO4 and CaF2 residues be separated?