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A plant in Alsace recycles its acid effluent. How?

Posted on 19 July 2018.

Discover how the Cristal Group’s Thann plant is recycling its acid effluent. It recycles acid, gypsum and carbon dioxide.

In the global context of resource scarcity and global warming, many more manufacturers are introducing action plans to reduce their environmental footprint.

Among them is the Cristal Group, the world's leading producer of titanium dioxide (TiO2). This white pigment, extracted from an ore (rutile), is used for various applications in the paint, paper, plastic and rubber industries. One of the seven sites where the Group produces TiO2 is in the town of Thann, in Alsace.

Neutralizing the acid in its effluent

The Thann plant uses sulfuric acid to extract TiO2 from rutile ore. At the end of the production process, this acid is obviously found in the effluent. Before the water returns to the natural environment, it is treated in such a way that the acid is neutralized. It turns out that this treatment produces gypsum, a mineral compound which is a byproduct of calcium sulfate neutralization and can be used in cement and plaster. Until now, depending on its quality, the gypsum was recovered and stored on a spoil tip or used in cement or plaster. However, an additional recycling sector has been set up for agricultural use.

In 2017, the plant decided to improve the management of its environmental impact. It therefore offered Veolia a 5-year contract to take over and optimize its acid effluent treatment plant.

Three recycling approaches

Veolia proposed an innovative approach based circular economy processes. These processes will make it possible to recycle the by-products generated by the plant in three different ways.

Firstly, Veolia aims to increase the amount of gypsum used, in particular by making this resource available on the local market. Secondly, through a nanofiltration and evaporation-concentration process, some of the sulfuric acid in the effluent will be recovered and recycled. Once purified, it can be re-used in the TiO2 production process - a circular economy loop which allows the plant to extend the life of the acid it uses in its production process. And thirdly, Veolia has suggested setting up a sodium or potassium bicarbonate production module, using the CO2 generated when neutralizing the acid in the effluent.

To sum up, from the waste the Thann plant produces - the acid effluent from TiO2 production - and the CO2 it emits, it will produce three valuable resources: acid, gypsum and sodium or potassium bicarbonate. A short circular economy loop that could well inspire other industries in the Alsace region!