Removing fluorine and chlorine from zinc oxide dust by wet alkaline washing and studying fluorine occurrence states

Abstract When zinc hydrometallurgy is used to treat zinc oxide dust (ZOD), the fluorine (F) and chlorine (Cl) in the dust interfere with zinc electrowinning. To investigate the effectiveness of F and Cl removal from ZOD by different alkaline washing methods. Under the condition that 16 g/L Na 2 CO 3 was mixed with 6 g/L NaOH in equal volume 1:1 and reacted with the dust under the optimum condition of the liquid-solid ratio of 5 mL/g for 2 h at 70 °C, final pH of 10, and stirring intensity of 400 rpm, the dechlorination of cloth bag zinc oxide dust (CBZOD) and boiler zinc oxide dust (BZOD) were 94.81 % and 90.63 %, respectively, and the defluorination were 84.81 % and 24.50 %, respectively. To further reveal the reasons for the difficult removal of F from ZOD, a step extraction method and physical phase analysis of residue were used, which resulted in more than 98 % removable fluoride in CBZOD and up to 56 % insoluble residue in BZOD. Therefore, it is obvious that the removal effect is better due to the presence of large amounts of removable fluoride and chloride in CBZOD; the F states and percentage of insoluble fluoride are main reasons affecting the removal of F.