Abstract
In this paper, various metal ions were utilized for the demulsification of spent metalworking fluids discharged from an automobile parts workshop. Five types of metal ions, i.e., Fe3+, Al3+, Fe2+, Ca2+ and Mg2+, combined with coagulant were systematically evaluated, and the synergistic effect as well as the optimum operating conditions were studied. The results indicated that the Ca2+ as well Mg2+ possessed hardly efficiency for the demulsification, on the contrary, Fe2+ reduced the yield of the by-product sludge and lowered the SV30 ratio, and Al3+ boosted the CODCr removal. Furthermore, Fe3+ and Al3+ had a significant synergistic effect to achieve a better transmittance and a higher CODCr/SV30 ratio which revealed that more CODCr was removed, as well as less by-product sludge was generated. For a better demulsification of spent metalworking fluids, the optimum operating conditions were gathered as follows: the dosage of metal ions was 0.08 mol/L with Al3+:Fe3+ ratio was 1.5:1, the reaction pH was 6.00, the reaction time was 18.00 min and the temperature was 323.00 K. Based on this, the CODCr removal, the SV30 ratio and the transmittance and CODCr/SV30 ratio of the spent metalworking fluids were 80.21%, 40.00%, 95.20% and 128.33 mg/mL, respectively. This combined metal ion demulsification method possessed an advantageous minimization of spent metalworking fluids, which greatly benefited the automobile parts workshops in cutting down the operating cost in environmental protection.
Highlights
Metalworking fluids (MWFs), which are a complex of oiling, surfactants and a variety of functional additives in accordance with a certain proportion of fusion, are abundantly utilized in the manufacturing domain and exert outstanding cooling, lubrication, anti-rust and anticorrosion protection functions [1,2]
According to China’s National Hazardous Waste List (2021 edition), longtime-used MWFs (L-MWFs) are the most significant waste discharged from the manufacturing workshop, which are labeled as Hazardous Waste (HW09, 900-006-09) [6]
This study provides a timely demulsification method with an attractive economy
Summary
Metalworking fluids (MWFs), which are a complex of oiling, surfactants and a variety of functional additives in accordance with a certain proportion of fusion, are abundantly utilized in the manufacturing domain and exert outstanding cooling, lubrication, anti-rust and anticorrosion protection functions [1,2]. After a long duration of repeating, attributed to the oil emulsion, residual metal chips, bacteria and the mix foreign material, the MWFs will gradually age, deteriorate and corrupt [3]. Those long-used metalworking fluids are hazardous to the equipment and emit a foul odor throughout the manufacturing workshop, which worsens the atmosphere conditions as well as the work environment [4]. According to China’s National Hazardous Waste List (2021 edition), L-MWFs are the most significant waste discharged from the manufacturing workshop, which are labeled as Hazardous Waste (HW09, 900-006-09) [6] Those hazardous wastes were forbidden to be discharged into the environment and should be strictly supervised and safely
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