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1.6 Sodium sulphate
1.6.1 General <strong>information</strong>
The production of natural sodium sulphate (like <strong>the</strong> production of natural NaCl or CaSO4) is
based on <strong>the</strong> extraction of a mineral with high content of sodium sulphate and its recovery in a
high purity grade through successive crystallisation/separation stages. This type of extractive
industry is not classified by <strong>the</strong> IPPC Directive and, <strong>the</strong>refore, it is not included in this
document. There are four producers of natural sodium sulphate in <strong>the</strong> EU-15, all of <strong>the</strong>m located
in Spain and <strong>the</strong>ir emission values have not been included in this section.
1.6.1.1 Introduction
The world production of sodium sulphate (anhydrous or as Glauber’s salt – sodium sulphate
decahydrate Na2SO4 . 10H2O) was reported to be at <strong>the</strong> level of 4.2 million tonnes per year in
1985, out of which almost 50 % was produced from natural deposits [48, W. Buchner et al,
1989]. The production of pure sodium sulphate or Glauber’s salt from natural minerals such as
<strong>the</strong>nardite Na2SO4 or glauberite Na2SO4 . CaSO4 is still important in Spain, Canada, <strong>the</strong> US,
Russia and China. O<strong>the</strong>r production processes of sodium sulphate from salt lakes, salt brines
and potassium salt deposits (in this latter case via reaction of kieserite MgSO4 . H2O with sodium
chloride NaCl), and in particular, sodium sulphate by-produced in large quantities in various
chemical and metallurgical processes are increasing [48, W. Buchner et al, 1989].
Sodium sulphate is a solid salt having wide range of applications in miscellaneous industrial
sectors like detergents, glass production or cellulose fibres [6, CEFIC, 2002]. Half of <strong>the</strong>
production is extracted from natural deposits while <strong>the</strong> remaining part is a by-product of o<strong>the</strong>r
industrial chemical processes, usually resulting from <strong>the</strong> neutralisation of excess sulphuric acid.
Therefore, <strong>the</strong> production of sodium sulphate may, in some places, exceed <strong>the</strong> commercial
demand, and processes have been developed to address this issue, using e.g. an electrochemical
decomposition route.
The direct production processes based on <strong>the</strong> reaction of solid sodium chloride with sulphuric
acid or sulphur dioxide/oxygen have become less important [EIPPCB, 2004-2005 #85].
Chemical processes like viscose-fibre spinning, ascorbic acid syn<strong>the</strong>sis or sodium dichromate
production, deliver aqueous solutions of sodium sulphate which are, if necessary, concentrated,
and <strong>the</strong>n directed to a crystallisation system which produces ei<strong>the</strong>r directly anhydrous sodium
sulphate crystals or Glauber salt crystals (sodium sulphate decahydrate Na2SO4 . 10H2O) that are
fur<strong>the</strong>r dehydrated. Electrolysis and electrodialysis processes intended to decompose sodium
sulphate into sulphuric acid and sodium hydroxide solutions, have been largely developed, but
<strong>the</strong>ir operational cost (e.g. <strong>the</strong> consumption of electricity) is an obstacle to <strong>the</strong>ir implementation.
Dust emissions to <strong>the</strong> atmosphere are <strong>the</strong> result of handling <strong>the</strong> solids. Water emissions include
dissolved salts.The generation of wastes is not an issue.
Organic contamination of air, water and wastes is to be considered, depending on <strong>the</strong> organic
process generating <strong>the</strong> sodium sulphate solution [6, CEFIC, 2002].
1.6.1.2 Basic data on sodium sulphate production
Sodium sulphate is a non toxic, hygroscopic white powder. It derives from natural deposits or is
recovered as a by-product from various industrial processes. Natural sodium sulphate is
extracted from sodium sulphate-rich brines or lakes, while <strong>the</strong> most common industrial sources
are <strong>the</strong> production of man-made fibres, hydrochloric acid, chromium chemicals, formic acid,
desulphurisation of flue-gases or lead battery recycling [64, CEFIC-SSPA, 2004].
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