A New Method for Production of Titanium Dioxide Pigment - Eliminating CO2 Emission

The objective of this project was to demonstrate the potential of a new process technology to reduce the energy consumption and CO{sub 2} emission from the production of titanium dioxide (TiO{sub 2}) pigment. TiO{sub 2} is one of the most commonly used minerals in the chemical manufacturing industry. It has been commercially processed as a pigment since the early 1900's, and has a wide variety of domestic and industrial applications. TiO{sub 2} pigment is currently produced primarily by the use of the so called �chloride process�. A key step of the chloride process relies on high temperature carbo-chlorination of TiO{sub 2} bearing raw materials, hence producing large quantities of CO{sub 2}. The new method uses a chemical/metallurgical sequential extraction methodology to produce pigment grade TiO{sub 2} from high-TiO{sub 2} slag. The specific project objectives were to 1) study and prove the scientific validity of the concept, 2) understand the primary chemical reactions and the efficiency of sequential extraction schemes, 3) determine the properties of TiO{sub 2} produced using the technology, and 4) model the energy consumptions and environmental benefits of the technology. These objectives were successfully met and a new process for producing commercial quality TiO{sub 2} pigment was developed and experimentally validated. The process features a unique combination of established metallurgical processes, including alkaline roasting of titania slag followed by leaching, solvent extraction, hydrolysis, and calcination. The caustic, acidic, and organic streams in the process will also be regenerated and reused in the process, greatly reducing environmental waste. The purpose and effect of each of these steps in producing purified TiO{sub 2} is detailed in the report. The levels of impurities in our pigment meet the requirements for commercial pigment, and are nearly equivalent to those of two commercial pigments. Solvent extraction with an amine extractant proved to be extremely effective in achieving these targets. A model plant producing 100,000 tons TiO{sub 2} per year was designed that would employ the new method of pigment manufacture. A flow sheet was developed and a mass and energy balance was performed. A comparison of the new process and the chloride process indicate that implementation of the new process in the US would result in a 21% decrease in energy consumption, an annual energy savings of 42.7 million GJ. The new process would reduce CO{sub 2} emissions by 21% in comparison to the chloride process, an annual reduction of 2.70 million tons of CO{sub 2}. Since the process equipment employed in the new process is well established in other industrial processes and the raw materials for the two processes are identical we believe the capital, labor and materials cost of production of pigment grade TiO{sub 2} using the new method would be at least equivalent to that of the chloride process. Additionally, it is likely that the operating costs will be lower by using the new process because of the reduced energy consumption. Although the new process technology is logical and feasible based on its chemistry, thermodynamic principles, and experimental results, its development and refinement through more rigorous and comprehensive research at the kilogram scale is needed to establish it as a competitive industrial process. The effect of the recycling of process streams on the final product quality should also be investigated. Further development would also help determine if the energy efficiency and the environmental benefits of the new process are indeed significantly better than current commercial methods of pigment manufacture.