Process for recovery of fluoride from wastewater produced in crystalline silicon solar cell manufacturing

A method for processing fluoride-containing wastewaters from a factory, comprising the following steps:

• Step 1:
• collecting the fluoride-containing wastewaters into three pools:
• an acidic high-fluoride wastewater that contains fluoride at a concentration higher than a first threshold concentration, an acidic low-fluoride wastewater that contains fluoride at a concentration lower than a second threshold concentration which is less than or equal to the first threshold concentration, and an alkaline wastewater;
• Step 2:
• adding a calcium compound to a portion of the acidic low-fluoride wastewater to produce a calcium-containing solution that contains calcium at a concentration of about 10-300 g/L;
• Step 3:
• reacting a portion of the calcium-containing solution with the acidic high-fluoride wastewater at a calcium-to-fluoride molar ratio of from about 0.5:1 to about 1.5:1 to produce a mixture comprising calcium fluoride particles suspended in a mother liquor;
• Step 4:
• processing the mixture to separately collect the calcium fluoride particles and the mother liquor;
• Step 5:
• diluting the mother liquor with a diluent to produce a mixed solution having a pH value of about 2-6 and containing a fluoride concentration of about 80-500 mg/L;
• and
• Step 6:
• introducing the mixed solution from Step 5, a remaining portion of calcium-containing solution from Step 2 which is not reacted in Step 3, and the alkaline wastewater from Step 1 into a fluidized bed reactor, which contains a calcium fluoride crystallization seed material, to form calcium fluoride crystals, wherein the alkaline wastewater is used to adjust a pH of a fluid in the fluidized bed reactor to a value between 5 and 8, wherein a molar ratio between the calcium in the calcium containing solution from Step 2 and the fluoride in the mixed solution from Step 5 is controlled at 0.5:1 to 2:1, wherein an effluent from the fluidized bed reactor is added to an inlet of the fluidized bed reactor to control a fluoride concentration at 150 mg/L or lower in an inlet region of the fluidized bed reactor, wherein a flow rate in the fluidized bed reactor is controlled at 100-20,000 m/hr.