Oxidation of Cr3+ to Cr6+ by hydroxyl radicals in leather

This study assesses the role of hydroxyl radicals (•OH) on the formation of Cr 6+ in leather. To avoid the complexity of composition of chemicals produced in leather fatliquors, •OH produced from the oxidation of lipids in leather fatliquors was replaced by •OH produced by a Fenton reagent. At room temperature, Fenton reagent was reacted with solutions of CrCl 3 , CrCl 3 - benzoic acid, chrome tanning agent and chrome tanning agent-benzoic acid, respectively. The amount of Cr 6+ in each solution was measured at different time intervals. The effect of •OH on the amounts of Cr 6+ was explored and the effect of adding an •OH scavenger(benzoic acid) on inhibiting the formation of Cr 6+ was also studied. Using ultraviolet spectrometry, the molecular structure of benzoic acid was analysed both before and after oxidation by Fenton reagent or potassium dichromate. The oxidization of Cr 3+ by Fenton reagent was initially explored. The results showed that the •OH group can oxidize Cr 3+ to Cr 6+ in both systems of CrCl 3 and chrome tanning agent and the •OH scavenger can inhibit the production of Cr 6+ . When the amount of benzoic acid was 3wt.% of the chrome the Cr 6+ concentration was decreased by 99.3% in 90 minutes.