High silicon dioxide (SiO2) content sands are referred to as silica sands. Along with numerous other industrial applications, glassmaking uses these sands. In order to satisfy customer demands, raw sand must be processed. It can be cleaned, treated, sieved, and purified. After spending a week with the work team at Adwan Sand Processing Factory in Algeria, we will talk here about how to process and analyse sand so that it becomes usable in various industries, especially the glass industry.
Raw sand processing stages:
Initially, the raw sand is transported to the factory via trucks. The composition and the physico-chemical characteristics of raw sand varies according to its type and place of extraction. To guarantee a high SiO2 content, the necessary particle size, and a low impurity level, quality raw silica sand is carefully chosen, in this factory, four types of raw sand are used, named according to the places of their extraction: Sig, Aricha, Gor, and Hassi Messaoud; they are all regions of Algeria.
[Raw sand storage- Adwan Company. Mostaganem. Algerie (Self taken photo)]
The goal is to obtain industrial silica sand by processing raw sand that goes through the stages of purification, sieving, washing and drying. But before that, some analyses are carried out on different raw sand samples, for the purpose of determining the chemical composition of each sample. The mass ratios of the constituents in each of the four varieties of raw sand are displayed in the following table:
• Using hydrofluoric acid to analyse SiO2 in sand:
In a crucible, we put one gram of sand (total weight is "m") and twenty millilitres of hydrofluoric acid (HF). After that, we set the electric oven to low temperature and put the mixture in it until it dries. Once the contents of the crucible have evaporated and dried, we add 10 millilitres of the same acid (HF) once again. Following that, the crucible is heated to 1000°C for one hour in an oven, after allowing it to cool, the sample's weight is measured ("m1").
% SiO2= (m - m1) * 100 / m
SW - Sand Washing unit:
In this unit, the sand is sorted, washed and purified from small stone. It is then passed through spirals to remove heavy metals. After the washing stage, the properties of the sand change, as the proportions of metals and clay decrease, and the proportion of humidity increases. The mass ratios of the constituents in washed sand are displayed in the following table:
Briefly, in this unit (SW), the raw sand is separated into four parts, which are as follows: clay and small stones, medium sand (diameter between 0.7 mm and 5 mm), iron sand, and wet silica sand (diameter less than 0.7 mm).
Drying and sieving unit:
At this stage, the silica sand is separated according to the particle size, but the increase in humidity caused by the washing stage will be an obstacle and cause the sieve pores to close. So the wet silica sand is first dried in a rotary kiln before sieving. The mass ratios of the constituents in dried silica sand are displayed in the following table:
conclusion:
Most of the sales of silica sand in this factory go to glass factories. Raw sand contains impurities and the percentage of silica in it is insufficient to make good quality glass. Also, the amount of iron in raw sand make the glass lose its transparency and give it an undesirable colour. Therefore, washing operations are carried out to obtain the highest possible levels of silica in the sand as the analyses showed [Which we obtained from the Adwan Chemicals Company in Mostaganem Province - Algeria).]
References:
- Etude de l’influence physico-chimique de la qualité du sable sur le rendement de la filtration du silicate de sodium- ESSELIMANI Abdelhadi- Université de Mostaganem- Memoire de fin d'étude.
- A Life Cycle Assessment of Silica Sand: Comparing the Beneficiation Processes- Anamarija Grbeš
