The chemistry and properties of salts used as fluxes for recycling aluminum were studied. Many fluxing salts fall within the system nacl-kcl-alcl3-naf-kf-alf3, which has been shown to be a reciprocal system, with naf-kcl, kcl-alf3, and nacl-alf3 as the stable mixed- halide binaries. Twelve subsolidus compatibility tetrahedra were determined by x-ray analyses of samples heated in evacuated sealed tubes. X-ray measurements of quenched and annealed samples indicate that elpasolite, nominally k2naalf6, has a compositional range between 60 mol % na3alf6, 40 mol % k3alf6 and 25 mol % na3alf6, 75 mol % k3alf6. Improved x-ray powder data are given for kalf4, showing a previously reported structure to be essentially correct.