RVA‘s slag recycling process is a closed-loop system making minimal demands on the environment: there is no solid waste; water used for washing is recirculated; gaseous emissions are incinerated to harmless residues and ammonia gas is neutralized by dedicated scrubbers. A proprietary computerized control system monitors the production process to ensure that key variables remain within pre-defined limits and outputs meet stringent specifications. The process comprises four stages:

(1) Milling

Firstly, salt slag is milled with optional recirculation to liberate aluminium by eddy current separator and iron by magnet. Fine particulate from the mill plant is removed by a de-duster.

(2) Dissolution/Reaction

Next, the remaining salty material is introduced to a dissolution section where it is mixed with water (recovered later in the process). The ensuing slurry is pumped into pressurized reaction vessels where it is agitated as the reaction temperature rises. Gaseous reactants are produced including hydrogen, methane and ammonia. These are incinerated and exhausted from the stack. Energy from the waste gases is recovered for other parts of the process.

(3) Filtration

The residual from the reaction phase is conveyed to a belt filter. Brine and water are sucked out under vacuum, leaving the solid residue, Valoxy. Clean water and the water removed in the dissolution stage are used to washed the solids.

(4) Crystallization

Finally, the effluent brine continues to the crystallization section. NaCl and KCl are crystallized out of solution, initially separately and then in combination, under optimal conditions, to bring the salt mixture to the required specification. An in-line decanter increases the concentration of solids in the slurry and facilitating higher salt recovery. The final mixture salt is conveyed to storage bays for onward shipment back to the secondary aluminium refiners. Water recovered from the crystallizers is recirculated back to the dissolution section.

recycling