Minerals From The

Apart from water (H2O), the main constituents of seawater are the following (in g/kg water): chlorine (Cl) 19.0, sodium (Na) 10.5, sulphate (SO4) 2.6, magnesium (Mg) 1.3, calcium (Ca) 0.4 and potassium (K) 0.4. Blood has a somewhat similar collection of minerals.

The main material in a snail's shell and in coral is lime. The formation of these structures happens electrolytically by negatively charged organisms, such as snails, precipitating natural lime and magnesium in salt water.

These processes can be performed artificially using electrolysis.The method is effectively the same as that used in galvanizing. Agood conductor, usually a metal mesh which can also be used for reinforcement in the structure to be produced, is dropped in the sea and given a negative charge.This is the cathode. A positively charged conductor, an anode, of carbon or graphite is put into the sea close by. As the magnesium and calcium minerals are positively charged from the beginning, they are precipitated on to the metallic mesh. When the coating is thick enough the mesh is retrieved and transported to the building site.The mesh or cathode can have any form and possibilities are infinite.

There are many experiments nowadays around such seawater based industries, even using solar panels as sources of energy. There is evidence that this is an

Table 6.7 Materials pollution from the production of basic materials from non-metal mineral raw materials

Material

Emissions

Calcined lime

CO2, SO2, unspecified dust

Natural gypsum

SO2

Portland cement

CO2, SO2, PAH, NOx, Tl, Ni, quartz dust, unspecified dust

Glass

SO2, CaCl2, CO2, unspecified dust

Table 6.8 Embodied energy in basic materials from non-metallic mineral raw materials

Material

Temperature required in production (° C)

Embodied energy (MJ/kg)

Lime

900-1000

4.5-5.0

DC

Natural gypsum

200

1.2-1.4

<

Portland cement

1400-1500

3.6-4.0

EL

Geopolymeric cement

3.75

Glass, primary

1400

10.0

Glass, 50% recycled

1200

7.0

environmentally acceptable method for the production of lime-based structures (Ortega,1989).

In the processing of these raw materials, high process temperatures and fossil fuels are often used. Depending on the temperature level there is also a chance that impurities can evaporate into the air, such as the heavy metals nickel, thallium and cadmium. The environment is usually exposed to large amounts of dust of different types.

Many forms of silicon dioxide (SiO2), have to be seen as risks for the working climate. The main problem is dust from quartz where overexposure can lead to silicosis. The dust can be emitted from several sources such as bricks containing quartz, or the production of stone, cement, concrete, rockwool, glass, glasswool, ceiling paper (where the paper is coated with grains of quartz), paint, plastics and glue. Olivine sand is not dangerous and can be used instead of quartz sand at foundries. Quartz sand can be replaced by materials such as perlite and dolomite as a filling for plastics. Silicon dioxide dusts in the form of fossil meal and perlite are inert compounds and harmless apart from some irritant effect.

When producing cements and lime binders, workers are exposed to many different risks, depending upon the product, such as noise, vibrations and dust that can lead to allergies. Large amounts of the greenhouse gas carbon dioxide and acidifying sulphur dioxide are released. At the construction site workers will be exposed to irritants from dust and from additives in the materials. The form of dermatitis attributed to

Table 6.9 Process-related and energy-related emissions of carbon dioxide from the production of lime and cements

Types

(g CO2/kg)

Lime

750

Portland cement

860

Fly ash/Portland cement

670

Blast furnace slag/Portland cement

350

Geopolymeric cement

290

repeated skin contact with chromium ions in Portland cement presents a particular problem. This can be mitigated, as is now often done, by adding small quantities of iron sulphate.

Once in the building these materials are relatively harmless, and as waste they are considered inert. Exceptions to this are asbestos and boron substances which have a pollution risk during their entire lifespan. Gypsum products can also leave sulphuric residues. It should be noted that it is often the various additives to non-metallic mineral products that are problematic in the environment, see Table 6.10 (Andersson, 2002).

The non-metallic minerals are usually impossible or difficult to material recycle as they are usually in the form of new chemical compounds in the final material. Thus, new supplies nearly always have to be extracted. Sulphur though is an exception that can be smelted out easily.

All glass can be recycled by re-melting. Coloured glass can be difficult, and used glass must be cleaned of all impurities first.

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