Stillwater Mining Company’s concentrator utilizes a bulk sulfide flotation circuit to recover sulfide minerals including palladium (Pd) and platinum (Pt). Sulfide flotation is a recovery process which utilizes surface properties of sulfides to concentrate sulfide minerals such as those that contain Pd and Pt. This process includes several stages of crushing/grinding to liberate the sulfide minerals from the gangue material (non-sulfide material), followed by the addition of flotation reagents, and finally flotation stages to physically separate the sulfide minerals from the majority of the gangue material.
In the crushing/grinding stages, crushers and grinding mills are used to liberate the sulfide minerals from the gangue minerals. This is done in several steps to optimize the grinding efficiency without jeopardizing overall recovery of the Pd and Pt containing sulfide minerals. Crushers are used as the first stage of size reduction followed by grinding mills which contain steel grinding balls used to induce energy and breakage of the ore. Stillwater’s concentrator uses three different types of grinding mills in its concentrator; SAG Mill, Ball Mill, and Verti-Mill. Each mill has a specific function in optimizing grinding efficiency and overall recovery.
Immediately following each grinding stage, flotation reagents are added to aid in the separation of the Pd and Pt sulfide minerals from the gangue material. These reagents include Potassium Amyl Xanthate (Collector), 3477 (Collector), and Corboxymethylcellulose (depressant). The collectors adsorb on the surface of the sulfide minerals and render them hydrophobic (water resistant) while the depressant adsorbs on the surface of the gangue mineral talc rendering it hydrophilic (water affinitive). These flotation reagents are then allowed to condition for a limited amount of time prior to the flotation step.
Following optimum grinding and reagent addition, the slurry is exposed to the flotation process. In this process the slurry is agitated while air is induced into the system. This air naturally attaches to the now hydrophobic sulfide particles and causes them to float to the top of the slurry level forming a froth layer. This froth layer is then collected as concentrate and subjected to further “cleaning” flotation steps which continue to separate the sulfide minerals from the remaining gangue minerals.
Final concentrate from the concentration process contains 36 oz/ton Pd + Pt and contains 91.8% of the Pd + Pt that was originally fed to the mill. On average the Stillwater Concentrator mills 2,400 tons of ore per day containing approximately 0.6 oz/ton Pd + Pt. Overall, 91.8% of the Pt + Pd is recovered concentrating it into only 1.5% of the original mill feed weight.
Please click on any image at left to take a tour of Sitllwater Mining’s Concentrator.
Mining Tour |
)
)
)
)
)
)
)
)
