Alkaline-based leaching techniques are utilized for the production of pure WO3 from either scheelite or wolframite concentrates via conventional tungsten manufacturing methods, which require multistep solution cleaning. Although, WO3 is acidic in character, it is possible to dissolve WO3 in the form of poly-tungstate ions through the additions to the solution aiming to change WO3's ligand mantle. It is possible, by this method, to produce low-cost and pure WO3, via less process steps as compared to the alkaline-based classical methods. The chelate-added acidic leaching is carried out under atmospheric conditions, at low temperatures and without generating a waste stream. On the other hand, there is no need for an additional roasting step to expel sulfur when the associated minerals are pyritic in nature. In this study, the effects of chelate-added HCl leaching conditions (starting material: 54% WO3, 2.3% S -scheelite concentrate with pyrite-based associated minerals, particle size of the concentrate, temperature, acid concentration and the ratio of chelating agent [PO43-]) on the tungsten extraction efficiency are investigated. Results of the experimental work showed that it was possible to reach about 93% tungsten extraction efficiency by using a concentrate below 325 mesh in size and under the leaching conditions of; 70-80 degreesC, 2M HCl, 1/5 Sn, and [PO43-]/WO3 ratio of greater than or equal to 7.