TM 08 Soluble Salts Analysis

  Slip Production white wares 

The salts content of the raw clay has an effect on the flocculation and deflocculation properties of the suspended material. It may be desirable to maintain the natural salts concentration, depending upon the type of water used and the flocculation method.

Heavy clay product production

Soluble sulphates tend to be detrimental in heavy clay products, leading to scumming during drying and firing. Residual soluble salts within the fired product which leads to efflorescence, specifically in clay bricks. Clays can be treated with barium carbonate during the mixing stage on factories, which precipitates barium sulphate that has a low solubility in water. To determine the amount of barium to add the clays salt content needs to be measured.

Building foundation material

During the 1950’s and 60’s colliery waste in the form of black ash and red ash was presumed to be inert and was used by the building industry as rubble for building foundations.

Most of these ash materials contain significant amounts of sulphates, these react with groundwater to produce dilute sulphuric acid which in turn slowly dissolves the cement in the concrete and mortar. The reaction with the cement causes a change in size, which leads to the concrete cracking.

Good building practice utilising a series of impermeable membranes or a high cement to aggregate ratio, reduces this problem. Most British building societies refuse to give mortgages on properties which utilise in-fill with a high salts content.

Soluble salt content determination

Extract salts from clays by grinding the material to less than 150 microns and stir in cold water for an hour. Depending upon the material characteristics, slightly different extraction techniques are required, e.g. for coals a boiling technique is preferable.

Analytically a gravimetric determination of precipitated barium sulphate or a titration against barium chloride can be used.