Abstract: A method is provided for the wet surface treatment of titanium dioxide, in order to produce durable universal grade titanium dioxide rutile pigment with superior optical properties. The method is characterized in that, a hydrous zirconia and silica composite layer is co-precipitated at acidic pH. Then, a layer of alumina is precipitated under a range of pH required for complete precipitation above the initial composite layer. The upper pH limit of the slurry during the alumina precipitation can be well controlled to avoid any chance for dissolution or damage of the composite zirconia-silica layer formed. Zirconia-silica composite layers and alumina thus precipitated advantageously improve the competence of the layers formed over a TiO2 base and provide improved durability with superior optical performance. The total surface treatment cycle time and chemicals used are minimal compared to conventional methods. Improvements in throughput and washing efficiency are also realized.

Abstract: A method for the purification of spent sulfuric acid and particularly the purification of spent acid, from titanium dioxide rutile manufacture through a chloride route, is provided. In the chloride route of titanium dioxide manufacture, sulfuric acid is used to clean the un-reacted gaseous flow coming out of the oxidizer, so the spent acid mainly contains un-reacted Ti4+ ions, trace amounts of Fe3+ ions, and NO2 gas. Titanium phosphate can be precipitated using acidic and or alkaline phosphate-containing precipitants in stoichiometric amounts. The method can include the addition of cutting water. NO2 gas evolved during the reaction can be scrubbed in water. The resulting aqueous acid-rich portion, or supernatant, can be separated from the precipitated phosphates and is very clear. Evaporation under vacuum conditions can increase the sulfuric acid concentration. The resultant purified acid can be re-used.

Abstract: A method for the purification of spent sulfuric acid and particularly the purification of spent acid, from titanium dioxide rutile manufacture through a chloride route, is provided. In the chloride route of titanium dioxide manufacture, sulfuric acid is used to clean the un-reacted gaseous flow coming out of the oxidizer, so the spent acid mainly contains un-reacted Ti4+ ions, trace amounts of Fe3+ ions, and NO2 gas. Titanium phosphate can be precipitated using acidic and or alkaline phosphate-containing precipitants in stoichiometric amounts. The method can include the addition of cutting water to commence the precipitation in two or more steps, when an acidic precipitant is used, and in one step with half the volume of water when an alkaline precipitant is used.

Abstract: A method for the purification of spent sulfuric acid and particularly the purification of spent acid, from titanium dioxide rutile manufacture through a chloride route, is provided. In the chloride route of titanium dioxide manufacture, sulfuric acid is used to clean the un-reacted gaseous flow coming out of the oxidizer, so the spent acid mainly contains un-reacted Ti4+ ions, trace amounts of Fe3+ ions, and NO2 gas. Titanium phosphate can be precipitated using acidic and or alkaline phosphate-containing precipitants in stoichiometric amounts. The method can include the addition of cutting water. NO2 gas evolved during the reaction can be scrubbed in water. The resulting aqueous acid-rich portion, or supernatant, can be separated from the precipitated phosphates and is very clear. Evaporation under vacuum conditions can increase the sulfuric acid concentration. The resultant purified acid can be re-used.

Abstract: A method is provided for the wet surface treatment of titanium dioxide, in order to produce durable universal grade titanium dioxide rutile pigment with superior optical properties. The method is characterized in that, a hydrous zirconia and silica composite layer is co-precipitated at acidic pH. Then, a layer of alumina is precipitated under a range of pH required for complete precipitation above the initial composite layer. The upper pH limit of the slurry during the alumina precipitation can be well controlled to avoid any chance for dissolution or damage of the composite zirconia-silica layer formed. Zirconia-silica composite layers and alumina thus precipitated advantageously improve the competence of the layers formed over a TiO2 base and provide improved durability with superior optical performance. The total surface treatment cycle time and chemicals used are minimal compared to conventional methods. Improvements in throughput and washing efficiency are also realized.

Abstract: A method for the purification of spent sulfuric acid and particularly the purification of spent acid, from titanium dioxide rutile manufacture through a chloride route, is provided. In the chloride route of titanium dioxide manufacture, sulfuric acid is used to clean the un-reacted gaseous flow coming out of the oxidizer, so the spent acid mainly contains un-reacted Ti4+ ions, trace amounts of Fe3+ ions, and NO2 gas. Titanium phosphate can be precipitated using acidic and or alkaline phosphate-containing precipitants in stoichiometric amounts. The method can include the addition of cutting water to commence the precipitation in two or more steps, when an acidic precipitant is used, and in one step with half the volume of water when an alkaline precipitant is used.