Recovery of rhenium and molybdenum from a roaster fume scrubbing liquor by adsorption using activated carbon

Activated carbon was used to adsorb and concentrate rhenium and molybdenum from liquors (pH 6–8) produced from a pilot plant set up to scrub a fume generated by a molybdenite roaster. The kinetics of adsorption of Re and Mo relating the loading of Mo or Re (Qt) to concentration at time t (Ct) and carbon concentration (X) follows the rate equation:Qt=kCttmLog(X)where k is the rate constant, m is 0.90 and 1.0 for Mo and Re, respectively.The adsorption follows the Freundlich isotherm and is influenced by temperature and solution pH. The elution of metal values from the 300–400 g/L carbon loaded with 14.4 mg/g Re and 4.2 mg/g Mo by 1 M NH4OH at 95 °C could produce a concentrated liquor containing ~ 2.8–3.2 g/L Re and ~ 0.6–0.8 g/L Mo after 4 h (at 50–68% metal recovery). The batch elution of the same loaded carbon at 100 g/L concentration yielded a liquor of 1.2 g/L Re (at 91.5% elution efficiency) and 300 mg/L Mo (at 80% elution efficiency). Stripping of Re using NaOH (1–3 M) at 95 °C is not as effective as with NH4OH.

► Water-scrubbing liquors treated to pH 6-8 to remove As, sulphate and cations
► Treated liquors contain Re and Mo for carbon adsorption.
► New kinetic model was developed, showing effect of carbon concentration.
► Effective elution of Re and Mo by ammonia (1 M) at 95 °C
► Precipitation of calcium molybdate completely removes Mo from Mo–Re liquors.