The metal concentration can generally be reduced to below 1 mg/L. The bulk of the metal is removed in the form of pellets from the reactor. Effluent filtration is usually required to remove suspended 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 metal salts on the pellet bed consisting of carrier material, a driving force is created by a reagent dosage, usually a combination of caustic soda and soda ash to achieve the optimum conditions for crystallisation of the desired salt. The pellets grow and thus float at a lower point of the reactor.
At regular intervals, a quantity 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.
The Crystalactor is most suited to treat flows with metal concentrations between 50 mg/L and 2000 mg/L. The required low effluent concentrations are usually achieved by recycling the reactor effluent a number of times, depending on the initial concentration. In some situations the filter is in the recycle loop. In others it is sufficient to treat only the effluent that leaves the loop.