Sub-Product

Spent caustic is a waste industrial caustic solution that has become exhausted and is no longer useful (or spent). Spent caustics are made of sodium hydroxide or potassium hydroxide, water, and contaminants. The contaminants have consumed the majority of the Sodium or Potassium hydroxide and thus the caustic liquor is spent^[1].

Spent caustic concentration is typically: 

• Low concentration: 1-5% w/w
• Medium concentration: 5-15% w/w
• High concentration: 15-25% w/w

Density values and molarity of KOH solutions at 20°C are presented in the following table^[2]:

References

1. Wikipedia, Spent caustic.Brave Search Summarizer, 30^th Jul 2024, Potassium Hydroxide Solution.
2. Gosta Akerlof and Paul Bender: The Density of Aqueous Solutions of Potassium Hydroxide, Journal of the American Chemical Society 1941 63 (4), 1085-1088.