Cleaner Production

The technology developed involves the recovery of chromium from the spent tannery liquors and its reuse.

Tanning of hides is carried out with basic chromium sulfate, Cr(OH)SO4, at a pH of 3.5 to 4.0. After tanning the solution is discharged by gravity to a collection pit. The liquor is sieved during this transfer to remove particles and fibers that have come from the hides. The liquor is then pumped to the treatment tank and a calculated quantity of magnesium oxide is added with stirring until the pH reaches at least 8. The stirrer is switched off and the chromium precipitates as a compact sludge of Cr(OH)3. After settling the clear liquid is decanted off. The remaining sludge is dissolved by adding a calculated quantity of concentrated sulfuric acid (H2SO4) until a pH of 2.5 is reached. The liquor now contains Cr(OH)SO4 and is pumped back to a storage tank for reuse (Figure 1.9).

In conventional chrome tanning processes 20 to 40% of the chrome used is discharged into wastewaters. In the new process 95 to 98% of the waste Cr3+ can be recycled.

Was this article helpful?

0 0
DIY Battery Repair

DIY Battery Repair

You can now recondition your old batteries at home and bring them back to 100 percent of their working condition. This guide will enable you to revive All NiCd batteries regardless of brand and battery volt. It will give you the required information on how to re-energize and revive your NiCd batteries through the RVD process, charging method and charging guidelines.

Get My Free Ebook

Post a comment