Selective precipitation is the main process used to remove molybdenum from tungstate solutions by the tungsten industry in China. The process exploits the fact that molybdenum is a sulfophile whereas tungsten is an oxyphile. First, the sulfur ions replace oxygen and convert the molybdate to thiomolybdate, then a moderate amount of additives (copper compounds) are reacted with the thiomolybdate to form complex precipitates. We call the filtered wet precipitate “molybdenum-removal sludge”. The main components of the sludge are molybdenum, copper and sulfur, infiltrated by some amount of tungsten due tomechanical entrainment. Based on the fact that copper is a typical sulfophile, it is possible that copper ions can react withthe sulfur of the thiomolybdate, thus converting it to soluble molybdate. This is actually the reverse of molybdenum sulfuration process, so we therefore call it the “reverse sulfuration process.” Based on the leaching thermodynamics and structure characteristics of this kind of sludge, a new treatment process was developed in this work. About 90% of tungsten and 15% of molybdenum were washed out with ammonia water when the pH > 9. The recovery rate of molybdenum was close to 70% when a stoichiometric amount of copper ions (with sodium hydroxide 4 mol/L) were utilized for the reverse sulfurization leaching. The leaching rate of molybdenum obtained on leaching with 2 mol/L sodium hydroxide for 120 min at 80 °C and then fixing with copper chloride was 94.4%, and 87.67% of sulfur ions were fixed in the form of an amorphous Cu S compound.
An efficient method for removing and recovering molybdenum (Mo) from water was developed by using ZnFe 2 O 4 nanoparticles . The Mo adsorption displayed a nonlinear isotherm that fitted well with the Langmuir isotherm , showing limited adsorption sites on the surface of ZnFe 2 O 4 . The adsorption of Mo(VI) was dependent on solution pH. With increasing pH, the build-up of negative charges of both adsorbent and adsorbate led to enhanced electric repulsion between them. The K -edge XANES spectra for the adsorbents collected after Mo adsorption revealed that Mo(VI) was the predominant oxidation state sorbed on ZnFe 2 O 4 , indicating that the reduction of Mo(VI) did not occur on ZnFe 2 O 4 . The different peak positions of k-space and R-space shown in K-edge EXAFS spectra demonstrated that the adsorbed Mo could be bound on the surface or be slipped in the vacancy position of the ZnFe 2 O 4 crystal. Importantly, Mo could be efficiently adsorbed from photoelectric industrial wastewater and these adsorbed Mo anions were rapidly replaced by OH − ions, implying the potential for Mo removing and recovering in industrial wastewater.
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