TANTALUM, TIN AND TUNGSTEN

TIN, TUNGSTEN AND TANTALUM

Tantalum and tin minerals frequently (but not always) occur commercially together in hard rock deposits usually as pegmatite. Tin also occurs in alluvial deposits. In addition tantalum is always associated with niobium. Tungsten minerals occur commercially in hard rock deposits usually in pegmatites (wolframite) or contact metamorphic skarns(scheelite).

The chemical composition, physical properties and appearances of these minerals can be summarized in the following table:

mineral	Chemical formula	Specific gravity	Magnetic response	Electrostatic response	appearance
tantalite	(Fe, Mn) (Nb,Ta)2O6	6-8	Weakly magnetic	conductor	Dark grey opaque
microlite	(NaCa)2 Ta2O6	4-6	Non magnetic	conductor	Dark grey opaque
columbite	(Fe, Mn) (Nb,Ta)2O6	5.2	Weakly magnetic	conductor	Dark grey opaque
cassiterite	SnO2	7-7.1	Non magnetic	conductor	Light grey to dark grey opaque
wolframite	(Fe,Mn)WO4	7-7.5	Weakly magnetic	conductor	Black-brown opaque
scheelite	(Ca)WO4	5.9-6.1	Non magnetic	conductor	White – grey-cream opaque

The physical properties (specific gravity, magnetic and electrostatic response) listed above are used to concentrate and separate these minerals using gravity separation, magnetic separation and electrostatic separation respectively to a saleable product or as a feedstock for further processing.

As tantalum, tin and tungsten deposits are generally hard rock, and low grade (particularly tantalum), they are considerably more difficult to process than mineral sands. Mining is either open cut or underground and requires drilling and blasting. The broken rock then requires crushing and grinding to liberate the minerals prior to separation. In the process of comminution the liberated particles will generally not be rounded in shape but angular making their behavior in wet gravity separation more difficult. In addition the comminution processes will generate particles of a wide size range despite screening, including fines and slimes which will make gravity separation difficult. As a consequence tantalum recoveries and concentrate grades are much lower than for mineral sands, typically 60% and 30% respectively, while tin and tungsten are generally higher, although still not as high as mineral sands.

A typical tantalum / tin / tungsten crushing circuit consists of a grizzly screen which is fed from a run of mine (ROM) pad consisting of several ore types and grades which are blended to produce a steady feed. The grizzly undersize is broken up in a primary jaw crusher, with the jaw crusher product being further broken up in a secondary cone crusher. The secondary crushed ore is then often screened over a double deck vibrating with the screen undersize (-12mm) going to a crushed ore stockpile and the oversize going to a tertiary cone crusher which operates in closed circuit with the screen.

The crushed ore stockpile then feeds a grinding circuit typically consisting of either rod mills or ball mills or combinations of both of these in closed or open circuit with cyclones or screens. The objective of the grinding circuit should be to liberate the mineral without over-grinding, with valuable mineral being recovered as coarse as possible in the subsequent gravity circuits. The degree of grinding required will thus depend on the liberation characteristics of the minerals. If grinding is carried out in closed circuit with a screen /cyclone then the product sizing will be closer than if in open circuit. If cyclones are used the cyclone undersize (which is returned to the mill) will contain valuable heavy minerals due to the SG effect on cyclone classification. In order to avoid over grinding of this mineral it is usual to incorporate a gravity separation stage, to remove the mineral from the grinding circuit. If screens are used, this is not an issue as classification is by geometric properties only.

Depending on the mineral liberation characteristics conventional jigs such as the Russell jig or In Line Pressure Jig may be used if liberation is coarse enough (i.e. + 1mm) to recover a coarse product early.

Subsequent gravity separation circuits typically consist of spirals, shaking tables, Falcons, Kelsey jigs and Mozeley gravity separators (MGS) depending upon the grain and liberation size and duty (i.e. roughing, scavenging or cleaning). Screening and classification using vibrating screens and banana screens, hydrocyclones and hydrosizers are commonly employed to assist in gravity separation. Regrind mills are used in conjunction with these separators and screens and classifiers.

Flotation is often used to scavenge fine tin to produce a low grade concentrate, suitable for gravity upgrading, typically with an MGS.

Current major operating tin, tungsten and tantalum mines are as follows:

Australasia

Metals exploration, Metals X has a tin mine operating at renison on the west coast of Tasmani

Global Advanced Metals, GlobalAM has a tantalum mine operating at Wodgina,in the P;ilbara region of Western Australia

Deutsche Rohstoff , WCM has a scheelite mine operating at Wolfram Camp, near Dimbulah, NQ

Africa

There are small scale mines extracting tin, tungsten and tantalum in a variety of African countries, including DRC, Rwanda, Nigeria, Ethiopia and Mozambique. Many of these are basic labour intensive local operations.

Asia

China accounts for a significant amount of the world's tin, tungsten and tantalum mining. among the major producers in China is Yunnan Tin, Yunnan

Indonesia has two major tin producers, PT Timah, PTTM and PT Koba Tin, Koba Tin both of which have land and sea based tin mining operations on Bangka nearby islands

Americas

Minsur, Minsur has a tin mine operating at San Raphael, in the Andean region of Peru

TABOCA, TABOCA has a tin and tantalum mine operating at Pitinga in the Amazon region of Brazil

Europe

Almonty Industries, Almonty has a scheelite mine operating at Los Santos, in the Salamanca region of Spain