The exhaust Chrome tanning baths still contains an important amount of dissolved trivalent Chrome that has not fixed on leather: it generally represents the 15-25% of the total quantity of Basic Chrome Sulphate used for tanning.

The Chrome recovery plants designed and manufactured by Italprogetti, allow the recovery of the unfixed chrome, in order to reuse it in process, with considerable benefits both from an environmental and economic point of view.

The Chrome recovery allows to significantly reduce its concentration in tannery waste water, making it much easier to reach the discharge limits for the effluents. In addition, the contamination with Chromium of the sludge generated by the treatment plant diminishes drastically and its disposal becomes easier and cheaper.

The Chrome recovery leads also to an overall reduction of the consumption of Chromium Basic Sulphate and hence to a considerable economic saving on its purchasing.

A deep knowledge of the technical solutions and of technologies developed in over 30 years of activity has allowed Italprogetti to design and produce tens of chromium recovery plants, both for individual and for consortia tanneries.

The Italprogetti Chrome treatment process is based on a methodology widely tested all over the world and mainly composed by the following treatment steps:

  • Fine filtration Particulate solids of the baths are removed for reducing as much as possible the presence of extraneous solids in the final chrome liquor.

  • Oil&Grease Removal: If the chrome baths are particularly greasy (ie, if fatty hides are processed), a preliminary oil&grease removal phase is necessary

  • Chrome Precipitation: The pH of the baths is risen up to 8,0-8,5: soluble trivalent chrome precipitates as Chrome Hydroxide.

  • Chrome Filtration: Chrome hydroxide is filtered in a recessed chambers filterpress, where well dewatered chrome cakes are generated. The recovery rate of Chrome in filterpress is very high ( more than 97%): filtered waters, which contain a very low chrome concentration, can be collected with the other tannery streams.

  • Chrome Dissolution: The Chrome hydroxide is turned back to dissolved Basic Chrome Sulphate by dosing concentrated Sulfuric Acid. This reaction is carried out in a special mixed reactor and the acid fumes the develop inside that are conveyed in a vertical wet scrubber for their absorption.

  • Final Polishing: The chrome liquor obtained after the dissolution phase still contains impurities (particles of grease, calcium and magnesium sulphate, proteins). Before reusing that in the process, a final polishing treatment is warmly recommended. The liquid, suitably mixed with filter aids, is sent to a second filterpress  which retains the impurities from the chrome liquor.  After polishing, the filtered liquor is stored and it can be used in the tanning process.