Research on treatment and mechanism of salicylhydroxamic acid flotation wastewater by O3-BAF process
Salicylhydroxamic acid is an effective and selective collector for tungsten and molybdenum ores. However, the salicylhydroxamic acid flotation wastewater discharge may cause damage to the water environment for the residual processing reagents with poor biodegradability. Combined O 3 and biological aerated filter (BAF) has a well-known potential for removing refractory or toxic organic pollutants. Combined process of O 3 and BAF (O 3 -BAF) was applied to treat the simulated wastewater from W-Mo mineral processing in this study. Compared single ozonation to O 3 -BAF, various influencing factors were discussed like O 3 dosage, reaction time, initial pH value, gas–water ratio and organic loading. Meanwhile, degradation mechanism of salicylhydroxamic acid was reduced. Under the optimal experiment conditions as pH value 8, O 3 dosage 1.3 mg·L −1 , reaction time 15 min, the five-day biochemical oxygen demand (BOD 5 )/chemical oxygen demand of potassium dichromate (CODCr) value increased to from 0.19 to 0.35. The effluent was pumped to the following BAF process, when the optimal experiment conditions was organic load = 0.82 kgCODCr (m −3 ·d −1 ), gas-water ratio = 6:1, CODCr concentration of effluent was 28.92 mg·L −1 and the removal ratio was 86.26%, while the removal ratio could higher to 91.12% for the O 3 -BAF combined process. The effluent could meet the discharge and reuse emission standards requirements in China. UV-vis absorption spectra and high performance liquid chromatography showed the degradation pathway of salicylhydroxamic acid by ozone oxidation was salicylhydroxamic acid → salicylic acid + hydroxylamine → catechol → maleic → small molecular organic acid → carbon dioxide + water. Salicylhydroxamic acid (SHA) is considered as an effective and selective collector for flotation. Combined O 3 -BAF has a well-known potential for removing refractory or toxic organic pollutants. Degradation mechanisms of salicylhydroxamic acid was reduced. Effluent could not reach the discharge or reuse standard in China. The BOD 5 /CODCr value increased to 0.35 after only 15 min reaction, which could meet the requirement of the following biological treatment. The degradation pathway was deduced as the following: salicylhydroxamic acid → salicylic acid + hydroxylamine → catechol → maleic → small molecular organic acid → carbon dioxide + water.
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