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This document has not been fully peer reviewed and <strong>the</strong> <strong>information</strong> within is not validated nor endorsed by <strong>the</strong> TWG on LVIC-S or by <strong>the</strong> European Commission, it is meant for <strong>information</strong>, only A flow scheme of <strong>the</strong> production sodium sulphate from <strong>the</strong> viscose-fibre process is given in Figure 1.10. 22 NaOH Steam Water Air Water Steam/gas/ brine Fibre production process Spinbath crystallization Calcination melting, dehydration Centrifuge Dryer / cooler Sieve Na 2 SO 4 product storage Vapour Condensate Water Filter Exhaust air Figure 1.10: Flow scheme of sodium sulphate production from <strong>the</strong> viscose-fibre process [64, CEFIC-SSPA, 2004] The raw material for <strong>the</strong> production of sodium sulphate is Glauber´s salt coming from spinbath crystallisation as a by-product of <strong>the</strong> viscose fibre process according to <strong>the</strong> equation above. The principle of <strong>the</strong> crystallisation process is to cool <strong>the</strong> spinbath from <strong>the</strong> production fibre to
This document has not been fully peer reviewed and <strong>the</strong> <strong>information</strong> within is not validated nor endorsed by <strong>the</strong> TWG on LVIC-S or by <strong>the</strong> European Commission, it is meant for <strong>information</strong>, only To change <strong>the</strong> sodium sulphate into <strong>the</strong> anhydrous <strong>the</strong>nardite form, <strong>the</strong> separated crystals must be suspended and heated with steam in a remelting vessel. Thus, <strong>the</strong> water leaves <strong>the</strong> sodium sulphate crystals. The crystals are separated from <strong>the</strong> mo<strong>the</strong>r liquid using centrifuges. The separated crystals are dried in a flash dryer and stored in different silos. For reasons of efficiency, <strong>the</strong> mo<strong>the</strong>r liquid from <strong>the</strong> sodium sulphate centrifuges is cooled and <strong>the</strong> additional crystallised Glauber’s salt is also brought to <strong>the</strong> remelting vessel. The primary mo<strong>the</strong>r liquid and part of <strong>the</strong> secondary mo<strong>the</strong>r liquid are purged to effluent. Steam is produced on <strong>the</strong> site using natural gas. The dryers are heated directly with natural gas. A flow scheme of sodium sulphate production by <strong>the</strong> Messo process is shown in Figure 1.11. Salt purge Cooling Remelting Drying Purge Steam Natural gas Recovery Purge Figure 1.11: Flow scheme of sodium sulphate production by <strong>the</strong> Messo process [64, CEFIC-SSPA, 2004] 1.6.2.3 Chromium process Sodium sulphate Crude sodium sulphate, a by-product from <strong>the</strong> sodium dichromate plant containing sexivalent chromium compounds (Cr +6 ), is dissolved and transferred into treatment tanks. At this stage, <strong>the</strong> solution is acidified in order to facilitate <strong>the</strong> chemical reduction of <strong>the</strong> solution using sulphur dioxide. After reduction, <strong>the</strong> pH is raised leaving an insoluble species of chromium suspended in a solution of sodium sulphate. This is filtered and <strong>the</strong> resulting solids are recycled back to <strong>the</strong> primary process of <strong>the</strong> production of sodium dichromate. The purified sodium sulphate solution goes forward subsequently into a crystalliser, centrifuge, dryer and classifier to form pure sodium sulphate crystals. A flow scheme of <strong>the</strong> production of sodium sulphate from <strong>the</strong> chromium process is given in Figure 1.12. 23
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Page 3 and 4: 2 PURIFICATION OF NON-FERTILISER GR
Page 5: List of tables Table 1.1: Typical c
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Page 48 and 49: References 41 Solvay S.A. (2003). "
Page 50 and 51: References 95 CEFIC-Brunner Mond (2
Page 52 and 53: Glossary SS Suspended Solids (conte
Page 54 and 55: Glossary Ca 2+ Calcium ion CaC2 Cal
Page 56: Glossary (NH4)2SO4 Ammonium sulphat

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