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DECEMBER 2018 I PCB007 MAGAZINE 67 to separate residual heavy metals such as nick- el and zinc. It should be noted that milder leaching chemistries such as glycine-peroxide solutions are being investigated [8] and have the poten- tial to reduce environmental impact. Even mild acids such as white vinegar can be used for leaching gold [9] . However, a stronger acid and oxidant are still needed along with addi- tional time or energy, and results are not suit- able for commercial scale. When it comes to recovering precious metals, the goal is always 100% recovery. Some progress is also being reported on improving extraction from hydro - metallurgical leaching solutions through the use of electroactive polymers. This requires additional active-bed processing but avoids the need for extraction reagents or addition - al energy [10] . In addition to hazardous wastes, hydro- metallurgical processes generate non-metal- lic waste, which is typically a mix of different plastic compounds that are not recyclable. A fraction may find its way to waste-to-energy fa- cilities, but the vast majority is trucked to land- fills. More advanced chemistries may also gen- erate waste that requires additional treatment for environmental disposal. Chart 2: Chemical recovery of PMs.