Mineral Resources, Economics and the Environment

Most environmental debates require an understanding of the fundamental principles of geochemistry that govern the movement of pollutants. These principles control environmental decisions in the same way that geological principles control the distribution of mineral deposits. Failure to understand them creates the risk of advocating impossible solutions, such as disposing of radioactive waste by burning it. Thus, before beginning our discussion of mineral resources, we must review the chemical controls that determine their environmental effects.

Principles of environmental geochemistry

Just in case you have forgotten some of your high school science, here is a quick review. The fundamental building blocks of Earth are atoms, which consist of a positively charged nucleus surrounded by a cloud of negatively charged electrons. The nucleus is made up of neutrons with no charge and protons with a positive charge equal to that of an electron. Different atoms, each with a specific number of protons, make up the elements, which are arranged in the periodic table (Figure 3.1). Elements lose or gain electrons to become ions. Those with fewer electrons than protons have a net positive charge and are known as cations; those with more electrons than protons have a net negative charge and are known as anions. Ions that lose electrons are said to be oxidized, whereas those that gain electrons are reduced. The valence or oxidation state of the ion refers to the number of electrons that it has lost or gained. Elements with different numbers of neutrons but the same number of protons are known as isotopes. They are commonly referred to by their number of protons plus neutrons, or mass number, and are written in the form 235U.

Atoms form chemical bonds with other atoms to produce compounds, substances with a definite chemical composition. A group of atoms is known as a molecule if it has no net charge, such as CO2, or a complex ion if it has a net charge, such as NH4+ or CO32–. Compounds are classified as organic if they contain carbon in association with hydrogen, oxygen, nitrogen, sulfur, phosphorous, chlorine, or fluorine, or inorganic if they do not contain carbon. Compounds that form during processes occurring in Earth are considered natural and those that are made in the laboratory are synthetic.