Results from Preliminary Tests on Reduction of Heavy Metals from Used Oil
The experimental data from preliminary tests showing ultrasonic irradiation effect on heavy metals are presented in Figures 4-3 to 4-7. The experiments were conducted by varying the operating conditions as mentioned in the last section. Metal determination by ICP-MS has a very low detection limit of ppb level, however, a big variation could be observed even in the same sample matrix when the sample that is taken and prepared for acid digestion is not taken from a homogeneous bulk. The results depicted in Figure 4-3 correspond to the ultrasonic irradiation experiments for identifying the effects of ultrasound and hydrogen peroxide on heavy metals, such as Ba, Cd, Cr, Pb, and Zn. Arsenic is not discussed here since it presented a very low concentration level in the original four used oil samples. In these experimental runs, the greatest reduction in metal content was observed when hydrogen peroxide was added to emulsified sample (A1-W-OH-US60). The effects of water (for creating emulsion) and hydrogen peroxide on heavy metal removal from used oil by ultrasonic irradiation are presented in Figure 4-4. The results indicate that the addition of hydrogen peroxide could only enhance heavy metal removal rate when extra water was added to the original used lube oil and mechanically emulsified. Extra water alone could not enhance the removal of heavy metal without adding hydrogen peroxide. The results also indicate that hydrogen peroxide is effective only when a certain amount of water is present.