The flowsheet below Explains the Extraction of Tin Ore as shown by a study adapted to the concentration of a lode tin deposit. Cassiterite (SnO2) is very friable and special considerations to crushing and grinding of the ore are necessary to avoid an excessive production of fines. The Mineral Jig is an important feature of this flowsheet to recover the coarse free tin mineral as soon as liberated.
The Tin Ore Processing Flowsheet
CRUSHING Circuit of Tin Ore
The crushing section is designed to remove the undersize between each crushing step to avoid an excess production of fines. This is accomplished by using a grizzly with ¼ inch spacings ahead of the Jaw Crusher. Also a Vibrating Screen is used ahead of the secondary crusher. The secondary crusher is operated in closed circuit with the vibrating screen to insure a uniform product to the plant.
SIZING AND GRINDING Tin Ore
Crushing and grinding tests on the ore show that by screening the minus 3/8 inch crushed ore at 6-mesh, approximately 50 percent weight of the feed containing appreciable amounts of free cassiterite could be effectively concentrated before any further size reduction.
Grinding is performed using a Rod Mill operating in closed circuit with a Vibrating Screen. This procedure provides a minus 20 mesh product for subsequent table treatment and minimizes overgrinding of the cassiterite. Depending on the characteristics of the ore, the possibility of using a Peripheral Discharge Rod Mill should be studied. Tramp oversize is removed by a Spiral Screen on the rod mill discharge.
The minus 6 mesh fraction of the ore and the rod mill discharge are concentrated by the Mineral Jig to recover the heavy, coarse minerals. The Mineral Jig which handles an unclassified feed is equipped with an end draw off arrangement for automatic discharge of the coarse (approximately +10 mesh) concentrates from the jig. The fine concentrates are discharged from the hutch using a Dowsett Density Control Valve.
The Mineral Jig tailing is pumped to a vibrating screen which returns the plus 20 mesh fraction to the rod mill for grinding.
HYDRAULIC CLASSIFICATION AND TIN TABLING
The minus 20 mesh screen undersize is sized in a Hydraulic Classifier for most efficient tabling. Concentrating Tables with sand riffles handle the coarser sizes while the finer sizes are treated on decks riffled for finer sands. The rougher table concentrates are subsequently cleaned on two separate tables. In some cases a portion of the rougher concentrate can be cut so as to yield some final concentrate not requiring retabling. Cleaner table middlings are returned to the hydraulic classifier while the rougher table middlings go to the grinding circuit after being dewatered in cyclone classifier. The overflow from the cyclone and hydraulic classifier are thickened prior to slime concentration.
The Buckman Tilting Concentrator is very effective to recover extremely fine cassiterite from the slimes. The concentrate is cleaned on a Concentrating Table and combined with the other tin concentrates.
TIN UPGRADING SECTION
The Mineral Jig and Table concentrates are sent to an upgrading section for the removal of the sulphides, magnetic iron, and other impurities. The gravity concentrates are ground to approximately 65 mesh, then treated by “Sub-A” Flotation to remove the sulfides.
In many cases this is a batch process using a Unit Flotation Cell. Flotation is usually at approximately 30 per cent solids and of sufficient time to remove the sulfides.
The Unit Cell underflow is dewatered on a pan filter and then dried on a batch dryer. The dried product is fed to a high intensity dry magnetic separator for removal of magnetic iron, and other magnetic susceptible minerals such as wolframite.
The above procedure will usually yield concentrates assaying 60 per cent tin or better with satisfactory recoveries of 70 per cent or better.
And finally, tin smelting.
Laboratory Concentrating Table is used in test work on tin ore to determine flowsheet.
Tin Beneficiation Summary
Description of the Ore
Cassiterite occurring in a siliceous iron oxide gangue and containing small amounts of pyrite.
Assay of Ore, Approximate Method of Process
Gravity concentration using Mineral Jig, Concentrating Table and Buckman Tilting Concentrator followed by “Sub-A” Flotation of the gravity concentrates to remove pyrite.
Flotation Reagents Xanthate, Z-5 and Pine Oil.