A process for extracting hydrogen fluoride from fluorine containing materials includes countercurrently contacting the materials with steam having a plane of rotation relatively perpendicular to the direction of flow of the material. An apparatus for the extraction of hydrogen fluoride from fluorine containing materials includes a rotary kiln having a first zone wherein a steam-air mixture countercurrently contacts the materials in an oxidation step, a second zone wherein an oxygen containing gas is tangentially injected into the kiln to provide complete combustion of carbon containing materials, a third zone wherein a steam stream countercurrently contacts the materials in a reducing step and means for providing a plane of rotation to the steam which is relatively perpendicular to the direction of flow of the material.
A method for recovery of fluoride values from spent potlining and fluoride containing insulating materials associated with the potlining is disclosed. Spent potlining and the insulating materials are reduced to a fine particle size and incinerated. The ash residue is leached with a dilute caustic and the leachate is treated with a calcium compound to precipitate calcium fluoride. The calcium fluoride is dried to a moisture content of less than 0.1 percent and is treated with about 93 to 99 percent concentration of sulfuric acid to produce hydrogen fluoride gas and a metal sulfate. The hydrogen fluoride gas is fed into an alumina dry scrubber to produce alumina with absorbed fluorides to be used as feed material to reduction cells used in the manufacture of aluminum by electrolytic reduction. The metal sulfate residue is treated with lime and constitutes an environmentally safe product which can be disposed of as landfill material.
This invention discloses processes for the treatment of coal and coal derivatives in order to remove contaminates to produce a high purity coal product. The processes generally comprise a sequential acid leaching in which a hydrofluoric acid leach is followed by a hydrochloric acid leach. The pyrite and other heavy metals from the coal are removed by physical separation, either gravity or magnetic separation. The leached coal is then treated either by a washing and drying step or by a heat treatment to remove volatile halides. The HF acid and the HCl acid leachates are recovered for regeneration of the respective leachates and are recycled for use in the leaching steps. In additional processing, the coal may be pre-treated by a mild HCl acid leach and by pre-drying or physical beneficiation of the coal feedstock.
A method is disclosed for detoxification of aluminum spent potliner by thermal treatment in a rotary kiln while blended with limestone and metal silicates to destroy cyanides and convert the soluble fluoride salts to relatively insoluble calcium fluoride and fluoride-bearing minerals, quenching the hot kiln discharge with an aqueous lime slurry to convert residual soluble fluoride salts on the particle surfaces to an insoluble form, and treating aqueous landfill runoff and capture with lime or limestone and recycling the treated water to the process. The treated material is suitable for landfilling in a non-hazardous waste landfill or marketing as a raw material. Air emissions are innocuous and there is no aqueous discharge.
