Mining Methods Vary Widely - Mining and the Environment: From Ore to Metal - page 225

tertiary crushing, and sizing. Screening is the single most important part of the processing
cycle of crushed stone particles. Stone washing is something performed in order to remove
unwanted material.
Sand and gravel deposits are commonly found in or adjacent to rivers or in areas with
glaciated or weathered rock. There are two main types of sand and gravel. Construction
sand and gravel are used mainly in concrete aggregates, road-base, asphaltic aggregates,
and construction i ll. Generally, the physical characteristics of construction sand and
gravel and their proximity to construction sites are more important than their chemical
characteristics. Construction sand and gravel represent some of the most accessible natural
resources and are major basic raw materials. Despite the low unit value of these products,
the construction sand and gravel industry is often a major contributor to and an indica-
tor of the economic wellbeing of a nation. While most countries have adequate sand and
gravel resources, this is not always the case. Singapore, for example, imports large quanti-
ties of sand and gravel from Indonesia, which has led to some sensitive political issues.
Industrial sand, gravel, and clay are used in manufacture of glass, ceramics, and chemicals.
The chemical and physical characteristics of these materials are very important to their end
uses, and are therefore subject to stricter chemical and physical characterization than construc-
tion sand and gravel. Loose sand and gravel deposits are usually mined without the necessity
of drilling and blasting. Material mined below water, in rivers, estuaries, lakes, and oceans
must be removed using specialized equipment such as dredges, draglines, and l oating cranes.
Common types of clay, ceramic, and refractory minerals include kaolin, ball clay, ben-
tonite, fuller's Earth, i re clay, common clay, and shale. Processing of minerals in this cat-
egory usually entails a combination of crushing, grinding, screening, and shredding to
reduce particle size. The cement industry consumes large quantities of clay and limestone,
and the occurrence of both raw materials in close proximity is an important criterion for
siting of cement plants. A cement producing operation is as much about mining as it is
about chemical processing ( Figure 5.2 ).
Chemical and fertilizer minerals include potash and phosphate rock. UNEP (2001)
provides an excellent summary on the chemical and fertilizer industry sector, and its
environmental challenges. Potash, a term that describes minerals containing potassium
compounds, is used in fertilizers. Processing potash involves mixing crushed potash ore

The construction sand and
gravel industry is often a major
contributor to and an indicator
of the economic wellbeing of a
nation.

FIGURE 5.2
Lime Stone Quarries Close to
Heidelberg, Germany

The cement industry consumes large
quantities of clay and limestone, and
the occurrence of both raw materi-
als in close proximity is an important
criterion for siting of cement plants.
Source:
Google Earth 2008