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Silica sand Geology and mineral planning factsheets for Scotland This factsheet provides an overview of Silica sand supply in Scotland. It is one of a series on geological issues in Scotland and is primarily intended to inform the land-use planning process. January 2006 S ilica (industrial) sands contain a high proportion of silica (up to 99% SiO 2 ) in the form of quartz and are used for applications other than as construc- tion aggregates. They are produced from both loosely consolidated sand deposits and by crushing weakly cemented sand- stones. Unlike construction sands, which are used for their physical properties alone, silica sands are valued for a com- bination of chemical and physical proper- ties. These include a high silica content in the form of quartz and, more importantly, low levels of deleterious impurities, par- ticularly clay, iron oxides and refractory minerals, such as chromite. They typically have a narrow grain-size distribution (generally in the range 0.5 to 0.1 mm). For most applications, silica sands have to conform to very closely defined speci- fications, and consistency in quality is of critical importance. Particular uses often require different combinations of proper- ties. Consequently, different grades of sil- ica sand are usually not interchangeable in use. Silica sands command a higher price than construction sands. This allows them to serve a wider geographical mar- ket, including exports. Demand Silica sands are essential raw materials for glassmaking and a wide range of other industrial and horticultural applications. Historically an important market for silica sand was in foundry casting. However, the progressive decline in UK heavy manufac- turing, and notably the foundry industry, has resulted in a significant decline in the demand for foundry sand. In contrast there has been a recent increase in demand for glass sand. In the UK in 2004 glass sand accounted for 53% of total sales of silica sand, foundry sand 11%, sand for other industrial uses 19% and sand for horticul- tural and leisure uses 17%. The main driver of silica sand demand in Scotland is the container glass industry. There are many different types of glass with different chemical and physical prop- erties. Most of the commercial glasses in everyday use, such as bottles and jars (containers), and flat glass (windows, mir- rors and vehicle glazing), are soda-lime-sil- ica glasses. These contain between 70–74% SiO 2 , the ultimate source of which is silica sand, although increasing amounts of sili- ca are being recovered in the form of recy- cled glass (known as cullet). Sand by itself can be fused to produce glass, but only at very high temperatures (1700°C). The addition of sodium carbonate (Na 2 CO 3 ) sig- nificantly reduces this temperature. Other components, such as calcium oxide (CaO), magnesium oxide (MgO) and alumina (Al 2 O 3 ) are added (in the form of limestone, dolomite and feldspathic minerals) in order to give the glass stability and dura- bility. Sodium carbonate is manufactured from salt and limestone, emphasising the Silica sand Geology and mineral planning factsheets for Scotland Lochaline Silica Sand Mine, Morven peninsula, Highlands. 1
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Page 1: Silica sand: Geology and mineral planning factsheets for ... › mlp › cd018.pdf · silica sand, the particle sizes required are coarser, with 0.5 to 1.0 mm being a popular grading.

Silica sand

Geology and mineral planning

factsheets for Scotland

This factsheet provides an overview of Silica sand supply in Scotland. It is one of a series on geological issues in Scotland and is primarily intended to inform the land-use planning process.

January 2006

Silica (industrial) sands contain a high proportion of silica (up to 99%

SiO2) in the form of quartz and are used for applications other than as construc-tion aggregates. They are produced from both loosely consolidated sand deposits and by crushing weakly cemented sand-stones. Unlike construction sands, which are used for their physical properties alone, silica sands are valued for a com-bination of chemical and physical proper-ties. These include a high silica content in the form of quartz and, more importantly, low levels of deleterious impurities, par-ticularly clay, iron oxides and refractory minerals, such as chromite. They typically have a narrow grain-size distribution (generally in the range 0.5 to 0.1 mm). For most applications, silica sands have to conform to very closely defined speci-fications, and consistency in quality is of critical importance. Particular uses often require different combinations of proper-ties. Consequently, different grades of sil-ica sand are usually not interchangeable in use. Silica sands command a higher price than construction sands. This allows them to serve a wider geographical mar-ket, including exports.

Demand

Silica sands are essential raw materials for glassmaking and a wide range of other industrial and horticultural applications. Historically an important market for silica sand was in foundry casting. However, the progressive decline in UK heavy manufac-turing, and notably the foundry industry, has resulted in a significant decline in the demand for foundry sand. In contrast there has been a recent increase in demand for glass sand. In the UK in 2004 glass sand accounted for 53% of total sales of silica sand, foundry sand 11%, sand for other industrial uses 19% and sand for horticul-tural and leisure uses 17%. The main driver

of silica sand demand in Scotland is the container glass industry.

There are many different types of glass with different chemical and physical prop-erties. Most of the commercial glasses in everyday use, such as bottles and jars (containers), and flat glass (windows, mir-rors and vehicle glazing), are soda-lime-sil-ica glasses. These contain between 70–74% SiO2, the ultimate source of which is silica sand, although increasing amounts of sili-ca are being recovered in the form of recy-cled glass (known as cullet). Sand by itself can be fused to produce glass, but only at very high temperatures (1700°C). The addition of sodium carbonate (Na2CO3) sig-nificantly reduces this temperature. Other components, such as calcium oxide (CaO), magnesium oxide (MgO) and alumina (Al2O3) are added (in the form of limestone, dolomite and feldspathic minerals) in order to give the glass stability and dura-bility. Sodium carbonate is manufactured from salt and limestone, emphasising the

Silica sand

Geology and mineral planning

factsheets for Scotland

Lochaline Silica Sand Mine, Morven peninsula, Highlands.

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Silica sand

Geology and mineral planning

factsheets for Scotland

dependence that some industries have on a number of industrial minerals.

The principal glass products using silica sand include colourless and coloured containers (bottles and jars), flat glass, light bulbs and fluorescent tubes, TV and computer screens, and glass fibre, both for insulation and reinforcement. Glass manufacturers are principally concerned with the chemical composition of silica sands, and particularly iron, chromite, and other refractory mineral contents. Quality requirements depend on the type of glass being manufactured (principally whether it is colourless or coloured) and to some extent on the requirements of the indi-vidual glass manufacturer. Glass sand for colourless glass containers generally has an iron content of <0.035% Fe2O3, for flat glass in the range 0.060 to 0.1% Fe2O3, and for coloured containers 0.2%–0.3% Fe2O3.However, it is the overall composition of the glass batch that is important and lower levels of iron in one component may be offset by higher levels in another. For example, the generally lower quality (i.e. higher iron) of colourless glass cullet has to be balanced by lower iron contents in the colourless glass sand.

In the foundry industry, silica sand is used as the main mould and coremaking material for both ferrous and non-fer-rous castings. The physical and chemical properties of the sand are important and depend on a number of factors, such as the metal and product being cast and the type of binder used. In the past naturally-bonded moulding sands were widely used. These contained sufficient clay to give the mould strength without the addition of a bonding agent. Today such sands are of little economic importance and demand is principally for clay-free (washed) sands, which are high in silica. They should also have a uniform (narrow) size distribution,

and grains with a generally high spheric-ity. A binding agent, either clay (usually bentonite) or a chemical, such as resin, is added to the sand.

Low iron silica sands, some of which are calcined (heat treated) to convert the quartz to cristobalite (a high temperature form of silica) are also ingredients of clay-based whiteware ceramic bodies, such as tableware, sanitaryware, and wall and floor tiles. They are also a component of ceramic glazes and enamels. Silica sand is the starting point for the manufacture of water-soluble sodium silicates, and other downstream silicon chemicals, such as silica gels, silicones, silanes and zeolites, which have a wide range of applications. In addition to a low iron content, a low alumina sand is also required for sodium silicates manufacture. In addition to being a component of glass, silica sand is also used as a grinding and polishing medium for the production of polished wired safety glass.

Other uses of silica sands include enhanc-ing the production (as proppants) of oil-field reservoirs, in the production of silica flour for use as fillers in plastics, paints and rubber sealants, and as fluidised bed boiler sands. Closely-sized grades of silica sand are the principal filtration medium used by the water industry to extract solids from water. In contrast to other grades of silica sand, the particle sizes required are coarser, with 0.5 to 1.0 mm being a popular grading. An increasingly important market for silica sand is sports and leisure applica-tions. Closely graded silica sand, in many cases mixed with organic matter, is used in top dressings and root zones for sports surface construction, for example for foot-ball and hockey pitches, and golf course tees and greens. Other uses of silica sand are for equestrian surfaces, for golf course bunkers, synthetic soccer pitches, as play

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Silica sand

Geology and mineral planning

factsheets for Scotland

sands and in horticultural applications demanding quality as well as consistency.

Supply

Scotland accounts for about 10% of UK silica sand supply with an estimated output of 473 000 tonnes in 2004, of which some 70% was glass sand (Figure 1). This is small compared with the total production of con-struction sand in Scotland (about 4.2 mil-lion tonnes in 2004). Recent data for silica sand sales in Scotland are confidential but the total appears to have been in the range 400 000 – 500 000 t/y (Figure 2).

With significant permitted reserves and unworked resources, Scotland may become of increasing importance as a source of silica sand for UK industry in the future.

Trade

International trade in silica sand is small.However, high purity silica sand is export-ed from the Lochaline Mine on the west coast of Scotland for uses such as in the manufacture of silicon carbide.

Data on inter-regional/national flows of silica sand within the UK are not available. However, glass sand from central Scotland is transported to Yorkshire for glass manu-facture and from the Lochaline Mine to Northern Ireland and the North West Region of England.

Consumption

Scotland is self-sufficient in silica sand with a total consumption of about 400 000 t/y.

Economic importance

The value of silica sand sales in Scotland was an estimated £6.5 million in 2004. No official figures are available for employment in the silica sand industry in Scotland.

Silica sand

Geology and mineral planning

factsheets for Scotland

Extraction

Glass sand

331 000 t

Construction sand

Processing: Washing, attrition scrubbing, sizeclassification, acid leaching, gravity and

magnetic separation

Colourless glasscontainers

EXTRACTION

PROCESSING

Foundry sand

30 000 t (e)

Other industrial

uses51 000 t

Agricultural, horticultural

& leisure uses

110 000 t

Colouredglass

containers

Figure 1 Scotland: Silica sand supply in

2005. (e) estimateSource: Minerals Extract in Great Britain, PA1007: Office for National Statistiscs.

0

100

200

300

400

500

600

700

1987 1989 1991 1993 1995 1997 1999 2001 2003 2005

Thousand tonnes

Figure 2 Scotland: Production of

silica sand, 1987–2005. Source: Mineral Extraction in Great Britain, PA1007: Office for National Statistics. Figures from 1997-2004 are BGS estimates.

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Silica sand

Geology and mineral planning

factsheets for Scotland

The glass industry is the most important consumer of silica sand, although the min-eral is consumed in many other sectors of the economy for the manufacture of value-added products.

Structure of the industry

The largest silica sand producer in the UK is WBB MINERALS Ltd, which accounts for well over 50% of total production and an even greater proportion of colour-less glass sand output. The company is a wholly-owned subsidiary of SCR Sibelco, a privately owned Belgian group with silica sand interests worldwide. The company only operates one site in Scotland, the Levenseat Quarry in West Lothian.

The other main silica sand producers in Scotland are:

Fife Silica Sands, a division of Patersons of Greenoakhill, Burrowine Quarry, Fife

O-I Devilla Forest Quarry, Fife Tarmac Group, Lochaline Mine, HighlandHugh King Ltd, Hullerhil Quarry, North

Ayrshire

A number of other companies supply small amounts of silica sand.

The Silica and Moulding Sands Association, part of the Quarry Products Association, is the trade association for the silica sand industry.

In Scotland glass containers are manufac-tured at Alloa and Irvine in central Scotland and glassfibre insulation at Stirling. The O-I glass sand operation at the Devilla Forest site in Fife is the only silica sand opera-tion in the UK that is owned by a glass manufacturer. Most of the sand output is used captively at O-I’s Alloa glass container plant.

Resources

Silica sands are produced from loosely consolidated sands and weakly cemented sandstones ranging from Recent to Carboniferous in age. Although sand and sandstone deposits are widely distributed in the UK, only a small proportion of these possess the desired physical and chemi-cal properties to be considered as poten-tial sources of silica sand. These, in turn, will differ appreciably in purity, particle size and thickness. All the sand resources will require some form of processing to upgrade them into marketable form. A criti-cal factor, therefore, in defining a sand or sandstone deposit as a silica sand resource is its inherent particle size and the ease with which impurities can be removed, together with the level of losses incurred in this process. The special characteris-tics of the markets for silica sand and the costs of processing, means that silica sand resources have a fairly restricted distribu-tion. In addition, resources that are suitable for one market may not be suitable for another. For example, glass sand suitable for the manufacture of colourless contain-ers is only capable of being produced at eight locations in the UK, four of which are in Scotland.

In Scotland the bulk of silica sand produc-tion is based on Carboniferous sandstones in central Scotland, although high purity silica sand of Upper Cretaceous age is also mined at the Lochaline Mine on the west coast of Scotland. The distribution of the main resources and glass plants is shown in Figure 3.

Extensive silica sand resources occur in central Scotland. These are princi-pally associated with medium to coarse- grained sandstones of the Passage Formation, which is Carboniferous in age. The Passage Formation comprises a

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Silica sand

Geology and mineral planning

factsheets for Scotland

cyclic sequence dominated by sandstones, which are white, grey and pale yellow in colour, but also includes mudstones, siltstones, seatearths and thin coals. The sandstones were deposited and then exposed to weathering in a humid tropi-cal environment, which resulted in the decomposition of less stable minerals to produce softer, friable sandstones com-posed mainly of quartz. The main silica sand sites are now located on the eastern side of the Central Basin, with large work-ings at Burrowine Moor and Devilla Forest in Fife, and Levenseat in West Lothian. The sands have a range of industrial and con-struction applications. The sandstones are also capable of processing to produce col-ourless glass sand with less than 0.035% Fe203. The operations in Fife supply con-tainer glass manufacturers in Scotland and Yorkshire. The sandstone resources of the Passage Formation appear to be relatively extensive and may become of increasing importance as a source of glass sand.

Small quantities of silica sand are pro-duced from sandstones within the Carboniferous Upper Limestone Formation at Hullerhill in North Ayrshire, and in the Douglasmuir Quartz Conglomerate Member, a hard, white Carboniferous con-glomerate in Strathclyde to the northwest of Glasgow.

The highest purity silica sand in Britain occurs in the Cretaceous-age Lochaline White Sandstone Formation in the Morvern peninsula and on the Isle of Mull on the west coast of Scotland. The sandstone consists of a very pure white to pale yel-low, well-sorted, medium-grained, quartz sandstone up to 12 m thick. The deposit is sub-horizontal and laterally extensive and has been preserved from erosion by a cov-ering of younger Palaeogene volcanics. It is extracted by underground mining at the

Lochaline Mine. After processing the sand contains 99.8% SiO2 and <0.014% Fe2O3

and most of the production is used in the container and domestic glassware market. However, the sand is also a key ingredient in the manufacture of silicon carbide abra-sives, borosilicate glass for laboratory and scientific use and chemical and domestic ovenware.

Silica sand

Principal Silica Sand resources

Openpit working

Mine

CarboniferousPassage Formation

Major Glass Plants

Container Glass

Insulation fibreglass

Lochaline Mine

Douglasmuir

Devilla Forest

Burrowine Moor

Gartverrie

LevenseatHullerhillIvy

Cottage

O-I, Alloa

Superglass Insulation,Stirling

Rockware Glass, Irvine

Figure 3 Principal silica sand resources in

Scotland.

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Silica sand

Geology and mineral planning

factsheets for Scotland

Reserves

In mineral planning, the term ‘reserves’ or ‘mineral reserves’ refers to material that has a valid planning permission for mineral extraction. Permitted reserves of silica sand include a wide range of differ-ent qualities, many of which are not inter-changeable in use.

No systematic survey of permitted reserves of silica sand in Scotland has been under-taken. However, permitted reserves within the Passage Formation of Central Scotland are of the order of 18 million tonnes, although this figure includes a range of qualities. At the Lochaline Mine permitted reserves and unconsented resources are reported to be some 40 million tonnes. However, this large potential cannot be

realised because the capacity of the mine is only about 150 000 t/y.

Processing plant for silica sand gener-ally requires a high capital investment. Sufficient permitted reserves are required to reflect this investment.

Relationship to environmental designa-

tions

No sites lie in national landscape designa-tions; some sites are locally constrained by nature conservation designations.

Extraction and processing

The extraction of silica sand is almost exclusively by surface quarrying. The only silica sand mine in the UK is at Lochaline in Scotland. Hard sandstone deposits are, wherever possible, now worked by rip-ping rather than by drilling and blasting. Loosely consolidated sands can be easily extracted. Worked thicknesses are up to 15 m for sandstone deposits. Some selec-tive extraction is required in the Passage Formation sandstones to avoid contami-nated sandstone and mudstone/siltstone beds.

At Lochaline access to the mine is by an adit located on the loch side. Mining is by room and pillar methods using drill and blast techniques to extract the sandstone, which is loaded onto dump trucks for trans-port to the processing plant on the loch side. Current working faces are about 900 m into the hillside. Although the sandstone is up 12 m thick only the middle 5 m of purer sandstone is extracted for process-ing. A hard sandstone band, together with the basalt lavas above, provides a stable roof. Annual production is some 100 000 t/y.

Silica sand processing is of varying degrees of complexity, and depends on the nature of the raw material and the end

Spirals for removing heavy minerals, Burrowine Moor Quarry, Fife.

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Silica sand

use of the sand. It typically requires a high capital investment in plant. Processing is aimed at improving both the physical and chemical properties of the sand to meet user specifications. Typically several grades of sand are produced from one site either by selective extraction and/or processing. At most operations processing involves washing, attrition scrubbing and size-clas-sification to remove the coarse and very fine fractions and to obtain a clean sand with the desired particle size distribution. Blending of lower and higher quality mate-rial is undertaken to optimise the use of the reserves. For the production of colourless glass sand, more sophisticated processing is required to remove contaminating impu-rities, either from the sand and/or from the surfaces of the individual sand grains. Gravity separation using spiral classifiers are used to remove heavy iron-bearing

minerals and chromite. Increasingly, how-ever, high intensity wet magnetic filters are being used to remove iron-bearing impurities, including mica. Hot sulphuric acid leaching is used at Devilla Forest in Scotland, to remove iron oxides coating the individual sand grains. Most foundry sands have to be supplied dried and drying facilities are a substantial capital invest-ment.

The extraction and processing of silica sand involves the production of only small amounts of waste. Yields of saleable prod-uct are on average about 90%, excluding overburden removal, which is used in site restoration.

By-products

Silica sand producers seek to maximise the use of the mineral in the ground and most

Levenseat Quarry, West Lothian.

Geology and mineral planning

factsheets for Scotland

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Silica sand

Geology and mineral planning

factsheets for Scotland

operations also produce some construc-tion sand as an ancillary, but important, by-product. A few construction sand quar-ries may also have an associated output of silica sand. Construction sand is produced from specific beds, including overburden, that cannot be processed to produce mar-ketable silica sand, and from coarse and fine material removed during processing.

Alternatives/recycling

Recycled glass (cullet) from bottles is increasingly used to make new glass. The use of cullet has a number of envi-ronmental benefits. It not only reduces the demand for new silica sand (and other components of the glass batch) but, because cullet melts more readily, it saves energy and also reduces emissions. Moreover, glass can be recycled more or less indefinitely. However, it is important that glasses of different colours are not mixed and that, as with silica sand, the cullet is free from impurities, in particular metals and ceramics. Currently the UK recycles some 37% of glass containers. There is a surplus of green cullet, some of which is exported and some used as an aggregate in materials such as asphalt. However, even with increased glass recy-cling rates the industry is still very short of colour separated cullet, a situation which is likely to get worse if the trend by local authorities to collect mixed cullet grows. Recycled, crushed and closely-sized glass from coloured bottles is also being developed as an alternative to sand for water filtration.

In the foundry industry most metal is cast in ‘greensand’ moulds in which a mixture of silica sand and bentonite is mixed with water to give sufficient plasticity for the mould to be formed. Volume producers of castings use automatic systems in which the used mould is disaggregated and the

sand recycled with a small addition of new bentonite to make good that destroyed in the casting process. Foundry sand used with chemical binders is also reclaimed using attrition and thermal processing and most is re-used with the addition of some new sand. Spent foundry sand is increasingly used for alternative applica-tions including as asphalt filler, in cement manufacture and in building blocks.

Effects of economic instruments

Silica sand that is used in prescribed indus-trial and agricultural processes is not sub-ject to the Aggregates Levy. Sands that are unsuitable for these applications are pro-duced as ancillary products at many silica sand sites and sold for construction use. These are subject to the Aggregates Levy.

Spent foundry sand is subject to the Landfill Tax. However, commercial pres-sures were already encouraging the re-use of foundry sand in other applications.

Transport

Most silica sand is transported by lorry and bulk tanker. Planning permission has been obtained at the Levenseat operation for a rail loading facility.

The Lochaline Mine is located on the coast and all of the output is transported by sea to destinations in England, Scotland, Northern Ireland and Norway using ships with capacities of some 2 200 tonnes. It is the only silica sand site in the UK with seaborne access.

Some consuming industries require deliv-eries to service 24-hour operations.

Planning issues

Compared to construction sand, silica sand has a number of distinctive charac-teristics which are relevant to land-use

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Silica sand

Geology and mineral planning

factsheets for Scotland

planning. These are:

the nature of the deposit worked is variable requiring flexibility in working arrangements;silica sand has a diverse range of appli-cations with many different specifica-tions;individual grades are often not inter-changeable in use;output volumes tend to be relatively low (<0.3 Mt/y in Scotland);other than glass cullet, there is a lack of alternative materials;the importance of the sand to a broad range of downstream, value-added man-ufacturing industries;the wider UK importance of silica sand supplies;processing plant is often complex and generally requires a high level of capital investment with associated high running costs;in some cases, processing plant oper-ates on a continuous (24 hours) basis;individual sites tend to be long-lasting;some silica sand resources can coincide with relatively sensitive environments and habitats;there is pressure to establish less dam-aging transport alternatives to road at well-established sites with long term futures; andsecurity of reserves is required to offset high capital and running costs.

Scottish Planning Policy 4: Planning for Minerals recognises the specialised nature of silica sands and their dependence on

the quality of the resource. It also recog-nises the wider significance of the market, notably for glass sand, and the need to safeguard unconsented resources against sterilisation by other forms of develop-ment.

Further information

Scottish Planning Policy: SPP4. Planning for Minerals.

Authorship and acknowledgements

This factsheet was produced by the British Geological Survey for the Scottish Executive.

It was compiled by David Highley, Andrew Bloodworth, Gill Norton and Paul Lusty (British Geological Survey) with the assistance of Don Cameron and Deborah Rayner (BGS).

The advice and assistance of the silica sand industry is gratefully acknowledged.

Geology Planning Factsheets for Scotland for a range of other geological issues are available for free download from www.mineralsUK.com

© Crown Copyright 2007

Unless otherwise stated all illustrations and photographs used in this factsheet are BGS© NERC. All rights reserved.

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