Results from Preliminary Tests on Reduction of Heavy Metals from Used Oil II
The comparison of the effects of ultrasound under oxidative and reduced environment is depicted in Figure 4-5. It indicates that hydrogen peroxide seemed to better in removing heavy metals than sodium borohydride (i.e., under reducing environment). For the set of experiments conducted using alkaline water (with addition of Na2SiO3) instead of distilled water to emulsify the used oil samples, the results, as shown in Figure 4-6 indicate that alkaline condition had very little effect in enhancing the removal of heavy metals from used oil. The results from the destructive adsorption process of removing heavy metals from used oils were depicted in Figure 4-7. Only Zn was selected as the target for measurement at this preliminary test run. It is clearly to see that either GAC or PAC is not a good selection for removing heavy metals from used oil. Both of them alone seemed not only unable to remove the heavy metals from used oil. When they combined with subsequent ultrasonic irradiation, the GAC test run can merely approach the same efficiency as ultrasonic irradiation run alone, however, the PAC test run indicates that the usage of PAC can alter the efficiency of heavy metal removal from used oil in a very undesirable direction. Though alumina alone can remove about 30% of Zn from used oil, however, when subsequent ultrasonic irradiation was applied, it did not improve the removal efficiency in a noticeable way compared to ultrasonic irradiation test run alone. Overall, silica gel seemed to perform superiorly in this destructive adsorption case since thoughitself alone cannot remove metal constituent from used oil, when subsequent ultrasonic irradiation was applied with silica gel still inside the used oil samples, it can enhance the removal efficiency of metal constituent from used oil almost 20% more.