Abstract: A method for removing dissolved fluoride from waste water involving a multiple stage process which includes a first step of contacting a solution comprising calcium fluoride with a calcium ion source to form a first precipitate and a second step of contacting the first precipitate comprising the calcium ion source with the fluoride-containing waste water solution to form a second precipitate. A first portion of the solution that has been treated directly with the waste water and which contains the second precipitate, is preferably recycled, along with calcium fluoride, to the first step for contact with the calcium ion source. A second portion of the solution treated with the waste water may be transported to a thickener or gravity settling step, and/or to a solids-dewatering step wherein standard filtration equipment may be used to produce a filter cake having a controlled particle size distribution.

Abstract: An industrial wastewater treatment method is described whereby heavy metals dissolved in the wastewater are precipitated as a slurry which, when allowed to settle, will form a sludge containing at least 10 weight percent solids. In the method, an aqueous suspension or solution of a neutralizing agent is introduced into a first reactor. A suspension containing particles of carrier agent is also introduced into the first reactor. A portion, if not all, of the neutralizing agent is adsorbed on the surface of the particles of the carrier, which are maintained in suspension in the first reactor. The carrier, with its adsorbed neutralizing agent, is passed to a second reactor and simultaneously the contaminated industrial wastewater is added to the second reactor. The pH of the wastewater is adjusted to a range between 8.4 and 10.6 by the neutralizing agent. Within such pH range, a substantial portion, if not all, of the heavy metals are precipitated in the form of a slurry.