Metal from Rocks

Elisabeth M. Price, Washoe County School District, Reno, Nevada

Dana Sue Kimbal, Newmont Mining Corporation

Introduction

This activity models a modern method for the extraction of gold and other precious metals such as silver from rocks.

The steps of the Washoe Process modeled here include the grinding and preparation of ore for extraction with mercury, and the reduction of the precious metal so it can be processed into the pure metal. The former step is the same as the modern preparation of the heap for leaching. In the Washoe Process, mercury was used to extract the metal from the rock. Mercury is too dangerous to use industrially or in the classroom, so in modern methods, cyanide is used for the extraction; however, in this model, extraction is carried out by simple water. The latter step of reducing the metal for processing is represented by the precipitation of the copper onto the iron paper clip. This step also models the reduction of the silver by the iron extraction pan in the Washoe Process.

KEY CONCEPT

Copper is leached from finely ground rock and recovered by reduction on iron paper clips. The activity models a heap leach pad and the modern procedures for recovering some metals, particularly gold and copper.

SKILLS: Observing, Recording, Investigating, and Modeling
TIME: 50 minutes
AUDIENCE: Teachers and students, grades 5 - 8.

OBJECTIVE

To understand the structure of a heap leach pad and the chemistry involved in leaching and recovering the metal from solution by making a model using copper as the recovered metal.

SAFETY

Wear chemical splash goggles.