Feasibility of the valorization of pMHS as pollutant trapper (CrVI) and validation as BAT

The metal finishing produces a significant quantity of metal hydroxide sludge (200 ktons) through precipitation treatment of their heavy metals charged liquid effluents. Generally, polymetallic sludge (without any majority species) are not given a great value because of their significant versatility in terms of metal content and are therefore sent in burying centers. This study refers to the promotion as adsorbent of these sludge to attach pollutants contained in industrial effluents. The pollutant of choice for this preliminary study is CrVI. A number of experimental parameters (chemical nature of the sludge, solid / liquid ratio, granulometry...) and two sorption methods (in stirring batch and in percolant batch) have been studied. It has been established that metal hydroxide sludge have significant adsorption capacities (elimination of up to 95 % of CrVI after 20 minutes of contact), depending on the experiment conditions. Furthermore, lixiviation capacities turned out to be potentially significant (up to 50% of the adsorbed CrVI is eventually released) according to the tested parameters. The sorption properties are compared to those of layered double hydroxides (LDH), that can be considered a perfect synthetic sludge. Similar adsorption capacities have been observed by comparison of the properties of these components (elimination of 95% of the initial CrVI), however the lixiviation capacities of LDH in the tested conditions are 10% max. this study has been completed by the assessment of the Val-Boue process against Best Available Techniques. The conclusion of this comparative study of this process and the classic dechromatisation technique is that Val-Boue is an emergent technique,candidate for BAT.