TDC offers sulfidic caustic solutions as an additional source of sodium and sulfur. Sulfidic caustics are typically highly alkaline sodium and sulfur solutions. Diesel or kerosene fuels, as an example, are treated or scrubbed with caustic soda to extract residual acidic impurities such as hydrogen sulfide (H₂S), mercaptans and organic acids. Sulfidic caustic may be used as supplement to pulping liquor for sodium and/or sulfur additions.