This publication is the fifth in a series of seven supplementary investigative materials for use in secondary science classes providing up-to-date research-related investigations. This unit is structured for grade levels 9 through 12. It is concerned with the removal of heavy divalent metals from water with the use of tannin-containing agricultural by-products. The first part of this guide provides the teacher with information about: (1) materials needed; (2) supplementary information; (3) preparation of peanut skins for use in the investigation; and (4) suggested readings. The second part provides students with background information and two investigations: (1) discovering an ion-exchange medium, and (2) scavenging heavy metals from solution. Each investigation consists of: (1) materials needed for a four-student team; (2) procedures; (3) questions for thought; (4) extending the investigation; and (5) suggested readings. (HM)