| Meningie Gypsum Quality Control |
| The Chemistry of Gypsum |
| Gypsum Regulations |
| Material Safety Datasheet |
MENINGIE GYPSUM QUALITY CONTROL
From the earliest days of exploration, right through to the screened product in our stockpiles, the company has not stinted in its obligation to provide current data to Primary Industries and Resources, customers and potential customers. Samples from our our minesites and our stockpiles are analysed regularly.
Careful analysis of exploration samples enables us to recognise potential gypsum resources and to reject other areas. Close spaced sampling within areas to be mined, and the analyses of these samples, aids our mining program. After screening our gypsum, samples from stockpiles are taken at regular intervals. Analysis of these enables us to monitor gypsum values, moisture content and salt levels. Our gypsum is not sold until it meets our exacting standards. Analyses include :
gypsum | CaSO4.2H2O |
calcium carbonate | CaCO3 |
magnesium carbonate | MgCO3 |
iron oxide | Fe2O3 |
aluminium oxide | Al2O3 |
sodium chloride | NaCl |
free moisture | H2O |
We do not analyse routinely for silica SiO2. The percentage may be approximated by subtracting the total of other components from 100. Any gypsum with a high silica content contains sand. Our gypsum has virtually no silica.
The analyses are provided by Australian Laboratory Services, a Brisbane based laboratory with NATA accreditation.
THE CHEMISTRY OF GYPSUM
Introduction
Pure gypsum consists of hydrated calcium sulphate: CaSO4.2H20.
% of calcium in pure gypsum: | 23.3% |
% of sulphur in pure gypsum: | 18.6% |
% of oxygen (in sulphate) in pure gypsum: | 37.2% |
% of fixed water in pure gypsum: | 20.9% |
Laboratories often assay for sulphur and convert the reading to gypsum.
Thus percent S x 5.38 = percent gypsum
and percent Gypsum x 0.186 = percent sulphur.
It is not legitimate to calculate the purity of gypsum from the calcium content, as calcium may be present also as lime, CaCO3.
The fixed water (water of crystallization, the 2H2O in the gypsum molecule) should not be confused with the moisture content of gypsum. Fixed water can be driven off between temperatures of 45oC and 128oC. When this happens, Plaster of Paris, CaSO4.0.5H2O is formed. On the other hand, all moisture in gypsum can be removed by heating up to 40oC. All assays are carried out after moisture is removed. Figures are for dry gypsum.
Impurities
Gypsum is a natural material, found in a number of geological environments, for example dunes and lake beds. Some even occurs as solid rock. Therefore various impurities may occur within it, for example, lime, clay, sand and salt. It is possible to work out which impurities are present by analysing the gypsum.
GYPSUM REGULATIONS
Primary Industries and Resources, South Australia formulated Regulation 201 (1999) of the Agricultural Chemicals Act (1955). Regulation 201 defines four grades of gypsum and demands that gypsum producers and marketers declare these grades and other factors, irrespective of whether the gypsum is supplied in a 10kg bag or as a 30 tonne truckload. The following GRADES are recognised:
Premium | Minimum 90% gypsum or 16.7% sulphur |
Grade 1 | Minimum 81% gypsum or 15.0% sulphur |
Grade 2 | Minimum 67% gypsum or 12.5% sulphur |
Grade 3 | Minimum 54% gypsum or 10.0% sulphur |
Salt content | NaCl less than 2%, (Na < 0.8%) otherwise warning required |
Moisture | The moisture content must be less than 15% |
Fineness | At least 50% of product must pass through a 2mm screen
At least 80% of product must pass through a 5.6mm screen |
Heavy metals | Should be less than 0.001% for cadmium
Should be less than 0.01% for lead |
These standards essentially conform with those of Victoria and New South Wales. However these eastern States of Australia do not define a Premium Grade. For non compliance, fines of up to $5 000 may be imposed in New South Wales and South Australia. In Victoria the maximum fine is $40 000.
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