Which process is used to recover precious metals from waste streams?

• A. Ion Exchange
• B. Electroplating
• C. Distillation
• D. Sedimentation

Answer: (A)

The process tested is about selectively removing and concentrating dissolved metal ions from watery waste so they can be recovered. Ion exchange uses a resin with functional groups that swap metal ions in the solution with ions on the resin. As the waste stream passes through, precious metal ions like gold, silver, or platinum bind to the resin while others stay in solution. The metals are then washed off (eluted) with a concentrated acid or other eluent to make a metal-rich solution that can be processed to recover the metal.

This approach is especially useful for dilute, complex waste streams because the resin can be chosen or conditioned to favor certain metal ions, and the bound metals can be released in a controlled, concentrated form for recovery or refining.

Distillation would separate components by volatility, but dissolved metals aren’t volatile, so it doesn’t remove them from solution. Sedimentation relies on settling of solids, not dissolved ions, so it can’t recover metals that remain in solution. Electroplating deposits metal onto a surface and isn’t a general method for pulling metals out of waste streams in bulk; it’s a coating process rather than a recovery method from solution.