On The Fenton´s Process for the Treatment of Effluents from the Dyeing of Agates Containing Rhodamine B and Ethanol

In the processing of agates, the gemstone pieces are submitted to dyeing processes. One of the dyeing processes applied is with Rhodamine B, which provides a reddish-pink colouration. The practice generates a wastewater containing residual amounts of the dye and ethylic alcohol with high polluting potential. Thus, the objective of this paper is to investigate the chemical parameters of the Fenton´s oxidation process to treat this effluent. The main parameters evaluated were [H ₂ O ₂ ]:[Fe ²⁺ ] molar ratio and the concentration of the reagents H ₂ O ₂ and FeSO ₄ .7H ₂ O. The wastewater contained a concentration of 772 mg L ^− 1 of Rhodamine B and 3% of ethanol in its composition, giving the effluent a high colour, organic load, and toxicity. In the Fenton reaction treatment, 11.1 g L ^− 1 of ferrous sulphate and 20 mL L ^− 1 of oxygen peroxide (in a molar ratio [H ₂ O ₂ ]:[Fe ²⁺ ] of 7.5:1) were defined as the best dosage, which allowed complete alcohol removal, an average absorbance reduction of 99.9% at 554 nm, a TOC reduction of 93.3%, an increase in surface tension from 58.9 to 64.4 mN m ^− 1 and a toxicity factor (TF) decrease from 526 to 16 with respect to the organism Daphnia similis . The Fenton process combines oxidation, coagulation and air stripping mechanisms that substantially reduces pollutants present in this effluent, at a rougher stage. The results obtained are useful, both for the gemstone sector and others that make use of Rhodamine B dye.