What recoverable chemical can be sourced from textile mill waste?

The recoverable chemical that can be sourced from textile mill waste is caustic soda. In the textile industry, caustic soda, or sodium hydroxide, is widely used in processes such as scouring and dyeing of textiles. During these processes, significant quantities of caustic soda can end up in waste streams.

Recovering caustic soda from textile mill waste is beneficial for both environmental compliance and economic reasons. The recycling of caustic soda reduces the need for fresh chemical input, thereby lowering operational costs. Furthermore, this recovery process helps in reducing the overall environmental impact of the mill's wastewater by minimizing harmful discharges.

Sodium chloride, vinegar, and sugar are not typically associated with specific recoverable processes within the context of textile mill waste. Sodium chloride might be present in some industries but is not a primary focus of recovery in this specific scenario. Vinegar, primarily acetic acid, is not derived from textile processes, and sugar is not related to textile manufacturing. Thus, caustic soda stands out as the correct answer due to its relevance and recoverability in the textile industry waste stream.