The Crystalactor technology removes fluoride from water in the form of calcium fluoride pellets by dosing lime, or a combination of caustic soda and calcium chloride as reagents. The fluoride concentration can be reduced to below 10-20 mg/L. The bulk of the fluoride is removed in the form of calcium fluoride pellets from the reactor and filtration is usually applied to polish suspended calcium fluoride flocs that are present as carry over from the reactor.
The heart of the Crystalactor treatment plant is the pellet reactor, partially filled with suitable carrier material such as sand, garnet, or small crushed pellets.
The water is pumped in an upward direction, maintaining the pellet bed in a fluidised state. In order to crystallise calcium fluoride on the pellet bed, a driving force is created by a reagent dosage. Usually fluoride flows have a low pH and an alkali needs to be dosed to convert all hydrogen fluoride into fluoride. In addition to this calcium is dosed to form calcium fluoride. Typically either lime, or a combination of caustic soda and calcium fluoride is applied.
The pellets grow and settle at the reactor bottom. At regular intervals, part of the largest fluidised pellets is discharged from the reactor and fresh carrier material is added. After atmospheric drying, easy-to-handle and virtually water-free pellets are obtained.
In most situations fluoride flows have concentrations in the range of grams per liter. The required low effluent concentrations are then achieved by recycling the reactor effluent a number of times. In some situations the filter is in the recycle loop. In others it is sufficient to treat only the effluent that leaves the loop.