Conceptual process design as a prerequisite for solving environmental problems; a case study of molybdenum removal and recovery from wastewater

Conceptual process design was used as a tool in solving an environmental problem concerning a molybdenum containing wastewater stream. The specific case involves a new styrene monomer plant that will generate a molybdenum (800–1000 ppm) wastewater stream also containing up to 30 g/l organics, 300 ppm aluminum and small amounts of heavy metals. A wastewater treatment plant was approached to investigate possibilities for treatment. The plant currently has an ion-exchange unit to treat similar waste streams, but its capacity is not adequate to treat an additional 330,000 ton/year. Disposal is not allowed and since molybdenum is a valuable metal, recovery as a saleable product is economically attractive. Two research groups from the Delft University of Technology applied the conceptual process design approach to analyze and solve the design problem, posed by the wastewater treatment company, from a wider perspective. As a result several recovery options were generated and analyzed. The process option that produces CaMoO4 by precipitation was selected as the most attractive molybdenum recovery process after evaluation of the designs against relevant quality factors like safety, economics, product market, environmental regulations and chemistry.