Low-fluoride wastewater recovery system

Abstract

A low-fluoride wastewater recovery system includes: a low-fluoride wastewater collection tank for containing low-fluoride wastewater; a fluoride adsorption device that interacts with the low-fluoride wastewater to form a first wastewater and a second wastewater; a separation device having at least one nanofiltration membrane to separate sodium chloride and sodium sulfate; a first crystallization drying device to form a first product (sodium chloride); a second crystallization drying device to form a second product (sodium sulfate); a bipolar membrane device to convert the second wastewater into an acidic wastewater and an alkaline solution, wherein the alkaline solution is recovered; a reaction tank to add calcium hydroxide to react with the acidic wastewater to form a third wastewater; a filtration device to convert the third wastewater into a third product; a drying device to dry the third product with a calcium fluoride purity greater than or equal to 97%; and a conversion device to convert the third product into a fourth product, acid-grade fluorite.

Claims

1. A low-fluoride wastewater recovery system, comprising: A low-fluoride wastewater collection tank for collecting and containing low-fluoride acid wastewater; a fluoride adsorption device connected to the low-fluoride wastewater collection tank, wherein the fluoride adsorption device interacts with the low-fluoride acid wastewater to form a first wastewater and a second wastewater, the first wastewater containing chloride ions (Cl–), sulfate ions (SO42–), sodium ions (Na+), and ammonium ions (NH4+), and the second wastewater containing sodium hydrofluoric acid (NaF); a separation device connected to the fluoride adsorption device, the separation device receiving the first wastewater, the separation device having at least one nanofiltration membrane separating sodium chloride and sodium sulfate from the first wastewater; a first crystallization drying device connected to the separation device, the first crystallization drying device forming a first product from the sodium chloride; and a second crystallization drying device connected to the separation device, the second crystallization drying device forming a second product from the sodium sulfate. A bipolar membrane device connected to the fluoride adsorption device receives the second wastewater and, under the action of an electric field, forms an acidic wastewater and an alkaline solution, the alkaline solution being recovered to the fluoride adsorption device; a reaction tank connected to the bipolar membrane device receives the acidic wastewater and adds calcium hydroxide to react with the acidic wastewater, forming a third wastewater containing calcium fluoride; a filtration device connected to the reaction tank precipitates the third wastewater into a third product; a drying device connected to the filtration device dries the third product, the calcium fluoride purity of the third product being greater than or equal to 97%; and a conversion device connected to the drying device converts the third product into a fourth product, the fourth product being acid-grade fluorite.

2. The low-fluoride wastewater recovery system as described in claim 1, wherein, It further includes a concentration unit connected to the bipolar membrane device and a third crystallization drying unit connected to the concentration unit. The concentration unit receives the second wastewater and concentrates it to form a fourth wastewater. The third crystallization drying unit receives the fourth wastewater and forms a fifth product, which is sodium fluoride.

3. The low-fluoride wastewater recovery system as described in claim 2, wherein, The concentration device is selected from any one or a combination of SWRO, EDR, and MVR.

4. The low-fluoride wastewater recovery system as described in claim 2, wherein, The sodium fluoride (NaF) concentration in the third wastewater is approximately 2-3%, while the sodium fluoride (NaF) concentration in the fourth wastewater is approximately 80% or more.

5. The low-fluoride wastewater recovery system as described in claim 1 or 2, wherein, The fluorine adsorption device includes an eluent selected from sodium hydroxide or the alkaline solution.

6. The low-fluoride wastewater recovery system as described in claim 5, wherein, The fluoride adsorption device has an exchange resin that captures fluoride ions to form the first wastewater, and then the fluoride ions are separated from the exchange resin by the eluent to form the second wastewater.

7. The low-fluoride wastewater recovery system as described in claim 1 or 2, wherein, The reaction tank is selected from a forced circulation crystallizer, a DTB crystallizer, or an OSLO crystallizer.

8. The low-fluoride wastewater recovery system as described in claim 1 or 2, wherein, The filtration device includes a tubular membrane and a filter press connected to the tubular membrane.

9. The low-fluoride wastewater recovery system as described in claim 1 or 2, wherein, The first product is sodium chloride, the second product is sodium sulfate, and the third product is calcium fluoride.

Images