In the commercial manufacture of titanium tetrachloride (for example, for the production therefrom of titanium metal or of pigmentary, chloride process titanium dioxide), a titanium-bearing ore, e.g., ilmenite, slag, synthetic or natural rutile, is chlorinated in the presence of coke as a reducing agent, conventionally in a fluid bed reactor at temperatures on the order of about 1000 degrees Celsius. In addition to the desired reaction product, namely titanium tetrachloride, other impurity metal values in the ore are continuously chlorinated to produce chlorides of iron, nickel, vanadium, manganese and other metals.
Conventionally, these waste metal chlorides are carried over in the chlorinator product stream with the desired titanium tetrachloride, with “blowover” ore and coke solids and with various byproduct gases such as carbon monoxide, carbon dioxide and the like. After passing through a heat exchanger, quench or similar to cool down the chlorinator product stream, the products of the chlorination step enter into a gas/solids separator, typically in the form of a cyclone separator. Waste metal chloride solids are removed with unreacted ore and coke solids from the bottom of the cyclone separator, as “cyclone dust”, “chlorinator waste solids” or similar. These chlorinator waste solids have been managed previously in a number of ways.
U.S. Pat. No. 5,271,910 to van der Meer et al. proposes leaching the cyclone dust in a hydrochloric acid-containing solution to obtain a solution containing substantially all of the impurity metal chlorides and a solids residue comprised of unreacted ore, silica and coke, performing a separation of the dissolved impurity metal chlorides and solids as by filtration, then precipitating the impurity metal chlorides as their hydroxides by neutralization, filtering to separate and recover the metal hydroxide solids and dewatering the filtercake thus obtained.
Schinkitz et al., in U.S. Pat. No. 5,334,362, describe a number of conventional approaches to the handling of chlorinator waste solids, before proposing an improvement of their own. As related by Schinkitz et al., one theretofore known process involved “pasting up and filtration” of the cyclone dust, whereby the filtrate of the suspension (chiefly being a solution of iron (II) chloride) is recoverable as a useful product for sludge conditioning in wastewater treatment and the coke-containing filtration residue or filtercake is disposed of or used as a fuel. A reported variation of this process, referenced to U.S. Pat. No. 3,655,344, involved “pasting up, neutralization and filtration” steps whereby the waste metal chlorides are converted to a water-insoluble solid metal hydroxide form and are disposable with the inert solids after filtration. The filtercake in this instance is described as “well filterable” and “non-thixotropic”, in contrast to the precipitated and worked up metal hydroxides which reportedly result from the process of EP 390 293 A1, wherein the inert solids—residual unreacted ore and coke in particular—are recovered for reuse prior to precipitation of the waste metal hydroxides and the filtration of the same.
Schinkitz et al. for their part propose an improvement to the process of EP 390 293 A1 whereby the useful inerts can be separated out, yet the waste metal hydroxides precipitated out under conditions such that a “well-filterable, non-thixotropic solid material” is reportedly obtained for landfilling. The examples reveal that with the inerts not recovered as in the first, known process the solids content of the filtercake from a filterpress is 46.5%, while in the second, known variation the solids content is reduced to 26.5%. Applying Schinkitz et al's improvement to the second variation yields however solids contents ranging from 37.7% to 39.0%. Schinkitz et al. acknowledge this difference, but point to reduced landfilling requirements overall by omitting the inert ore and coke solids from the filtercake and to improved economics through the recyclability or product value generally of the recovered inert solids fraction as more than offsetting the reduction in the achievable solids content of the filtercake.
U.S. Pat. No. 5,935,545 to Leary et al. quenches and slurries the cyclone dust with water, forming a cyclone underflow slurry of dissolved metal chlorides including most of the impurity metal chlorides, ore, coke and gangue solids. Hydrocyclone separators are suggested for recovering some of the ore which is recycled to the chlorinator. Ferric chloride and some other lower boiling metal chlorides are carried in the cyclone overflow, cooled and precipitated out, then separated out by any suitable gas-solid separation device.
U.S. Pat. No. 6,399,033 B1 to Hartmann (commonly-assigned with U.S. Pat. No. 5,334,362) utilizes a hydrocyclone to separate out a slurry of the cyclone dust solids into a titanium dioxide (ore)-rich underflow fraction and a coke and silica-rich overflow fraction, the overflow fraction being filtered in a belt filter or filter press to produce solids useful as a fuel and a filtrate suitable again for sludge conditioning in wastewater treatment. The underflow is likewise filtered in a belt filter or filter press, and the filtercake is dried and ground for recycle to the chlorinator while the filtrate is suggested for use in chemical treatment of wastewaters. By using a hydrocyclone on the cyclone dust then drying and grinding the solids in the hydrocyclone underflow, buildup of silica in the chlorinator bed is avoided from silica carried through in the cyclone dust.