What is the optimum pH for chrome reduction using sulfur dioxide?

The optimum pH for chrome reduction using sulfur dioxide is 2.0. At this pH level, sulfur dioxide effectively reduces hexavalent chromium (Cr(VI)) to trivalent chromium (Cr(III)). This reduction process is critical in wastewater treatment, particularly for effluents that contain toxic chromium species that must be neutralized before discharge.

At a low pH, the protonation of chromate (CrO4^2-) enhances its conversion to the less harmful Cr(III). Sulfur dioxide acts as a reducing agent in this environment, where the acidic medium optimally maintains the chemical reactions necessary for effective chrome reduction. This ensures better efficacy in treating wastewater that contains chromium pollutants, allowing for safer environment and compliance with regulatory standards.

In contrast, higher pH values can lead to the formation of stable chromate ions, hampering the reduction process and making treatment less effective. Thus, the choice of pH is fundamental to ensuring that sulfur dioxide can perform its role effectively in the reduction process.