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<p>The treatment of oxytetracycline (OTC) in test solutions by ferrate (VI) was investigated aiming to propose the effects of pH, concentration of co-existing ions and humic acid on the OTC removal. Ferrate (VI) can remove 97% OTC (from 1000 µg·l<sup>-1</sup>) in 30 minutes under the optimal conditions with solution pH of 7 and ferrate (VI) dosage of 20:1 as a molar ratio of ferrate (VI)/OTC. The effects of co-existing ions (0.005 mol·l<sup>-1</sup> and 0.02 mol·l<sup>-1</sup>) and humic acid (0.1~50 mg·l<sup>-1</sup>) on the OTC removal were investigated for the optimal operating conditions. The results showed that Ca<sup>2+</sup>, CO<sub>3</sub><sup>2-</sup>, PO<sub>4</sub><sup>3-</sup>could inhibit the OTC degradation and its removal rate decreased from 79, 29, 29% to 70, 19, 19%, for the ion concentration increased from 0.005<br />
mol·l<sup>-1</sup> to 0.02 mol·l<sup>-1</sup>. Mg<sup>2+</sup> and HCO<sub>3</sub><sup>-</sup> could restrain the reaction carried out at 0.02 mol·l<sup>-1</sup> and the removal rate was only 59%, 62%. Al<sup>3+</sup>could increase the removal rate which reach to 100%. Humic acid with concentrations of greater than 10 mg·l<sup>-1</sup> could notably inhibit the OTC removal. Regression analysis indicated good fit of the experimental date to the developed model with coefficient of determination (R<sup>2</sup>) value of 0.9991 and the adjusted R<sup>2</sup> value of 0.9978.</p>
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