Malawi Glass Sands

Abstract

Substantial deposits of glass sands occur in dambos around Mchinji. Recoverable reserves in six dambos amount to 1.6 million tonnes. Silica percentage for the sand varies from 96% to 99 % while the iron percentage varies from 0.12% to 0.2%. The deposits are suitable for the manufacture of good quality glass.  

The Lake Chiuta sand bar is estimated to have 25 million tonnes of glass sand containing 92.7% silica and 0.62% iron. Further beneficiation will improve the quality of the sand to make it suitable for the manufacture of plate glass and amber glass containers. Scrubbing and magnetic separation can lower iron percentage and unlock more production of other glass products.

  1. Introduction

Mchinji glass sands exist in dambos within Map Sheet 1332D4 of the Malawi Survey Maps.  They are  within 110 km range west of Lilongwe and about 8 km to the south of Lilongwe – Mchinji tarmac and railway line (Figure 1). The dambos are located at Sankhani, Samphale, Chitapalume, Kafulama, Tsumba, Elenesito (Kanjira), Ngoni, Kapepe, Kadu and Jailosi.

Lake Chilwa Sand Bar has over 92% of its quartz within a grain size of 120 and 30 mesh. 

Glass sand or silica sand is a natural raw material composed largely of the mineral quartz (60-80 % quartz).  The sand as raw material should have a grain size of between 0.1 mm and 0.3 mm (130 – 52 mesh size) and a chemical composition of Fe203 (iron oxide) content that does not exceed 0.040 percent The purity of the silica sand determines its color, strength, and clarity of the final product.

2.0    Silica sand deposits

Malawi has two types of silica sand deposits.  These are dambo sand and beach sand. Known deposits include Mchinji dambo sand and Lake Chilwa sand bar (Table 1).

The geology of the area around the dambos is characteristic of the Mchinji group (Thatcher and Wilderspin, 1968) which is composed of quartzite, quartz-schist, and pelitic schist (Figure 2).  The rocks are either fine-grained or coarse-grained.  The fine-grained type is a source of the silica sands found in the dambos.

Mchinji dambo sand is a product of fluvial accumulation at the head of dambo close to hills made up of quartzite schist and quartzo – feldspathic gneiss (Figure 1).

Lake Chilwa sand bar is a 10-20 metre raised beach and about 40 km in length. It is well sorted in the middle containing mainly quartz grains. This section contains about 25 million tonnes of glass sand (Figure 2). 

Both the western and eastern sections of the sand bar have very coarse to gravelly sand.

3.0    Economic assessment

For this to contribute to industrialization and urbanization, we can utilize the sand directly for production of glass sheet, plate glass and amber containers (Table 2). Further processing can lead to production of:

  1. Foundry mold (for producing metal parts)
  2. Glass manufacturing (flat sheets and fibre) 
  3. Artificial abrasives (sandpaper)
  4. Metallurgy 
  5. Chemicals (Sodium silicate, silicon tetrachloride, silicon gels)
  6. Ceramics, frits (glass materials) e.g., containers
  7. Roofing material (paint) 

This can be achieved using processing method shown in Figure 3 and reduction of iron content through scrubbing and magnetic separation. 

Together with iron and steel, glass sheets constitute a major proportion of modern buildings.

The project may not necessarily promote foreign direct investment as it involves an industrial mineral. It is a good candidate for import substitution of glass products and should be promoted by a State-owned enterprise to create jobs and promote new infrastructure development.

Glass sands are economically assessed through their chemical composition and physical characteristics.  The best quality sands have very high silica content and low iron/chromium content.  Iron and chromium have a colouring effect. Alumina makes the glass less transparent and makes melting difficult. A good sample should have a maximum Fe2O3 content of 0.06% and a maximum Al2O3 content of 0.1%.  In terms of physical characteristics, the sand grains need to be sub-angular and also uniform in size within 0.2 and 0.5mm in diameter.  This helps fast and even melt. Table 1 summarises specifications on chemical composition for glass sand as recommended by the Ceramic Society.

From the above chemical characteristics, it can be concluded that Mchinji dambo sand can be used in its raw form as a source for flint containers, sheet and plate glass, and coloured glass (See Table 1).  Further beneficiation can easily qualify them to be used for optical glass.   

4.0    Conclusion

Glass sand will constitute an important component in urbanizing Malawi. This will offer flat sheets complementing iron and steel in the construction of modern buildings and save the environment through less use of burnt bricks. Manufacturing of amber glass containers or bottles will be promoted creating wealth and employment. This will be made possible through public and private sector participation in partnership with a State-owned enterprise. This arrangement will help promote import substitution and empowerment of citizens through divesture of mature projects.

5.0    References

1.0    Boswell, P. G. H. 1918: British resources of sands and rocks used in glass making, 2nd Edition, Longman, Green and Co,

2.0    Crow, M. J. and Kayira, G, 1979: A preliminary assessment of the glass making potential of dambo sands south-east of Mchinji. Unpublished Report. Geol. Surv. Malawi T720.

3.0    Johnstone, S. J. and Johnstone, M. G. 1961: Minerals for the chemical and silica industries. Second Edition. Chapman and Hall 2, Sankhani 2, and Tsumba 2 dambos, Mchinji District.

4.0    Mndala, A. T. 1980: A provisional Estimation of reserves and quality of glass sands in parts of Samphale. Unpublished Report. Geol. Surv. Malawi T751.

5.0    Thatcher, E. C. and Wilderspin, K. E. 1968: The geology of the Mchinji-Upper Bua Area.  Bull. Geol. Surv. Malawi 24.

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