MINING CHEMICALS
Flottec laboratory for work on fine and coarse particle flotation at various bubble sizes and cell hydrodynamic conditions
Cappuccitti adds that great progress has also been made in the understanding of how reagents affect flotation hydrodynamics and therefore, flotation performance.“ In recent work that we conducted, we have shown that all reagents have some form of hydrodynamic characteristics. But we also concluded that although some collectors have frothing properties, when frothers are added, their properties dominate. This same work has provided even more convincing evidence that particles of different sizes float best when the pulp is at the minimum bubble size which occurs at the CCC of the particular frother and air rate used. The idea that small bubbles are needed for small particles and large bubbles for large particles may not be true. What is more important for flotation of fines versus coarse is the actual strength of the frother – weak frothers for fines, stronger frother for coarse. This understanding makes it much easier to design flotation circuits to improve recovery of all sizes of materials.”
Finally, another area of focus by Flottec is the use of reagents to control gas hold up in the flotation circuits.“ It is becoming evident that gas hold up in the cells is a prime driver of performance and therefore, if it can be measured and controlled, the circuits can be better operated at optimum conditions. Further work is required and planned in the next year.” More information on this work that is progressing on the control of flotation circuits will be featured in the November 2017 flotation edition of IM. previously developed CYANEX 272-specific SX modelling software to assist operators in the design and optimisation of their circuits. The modelling software has enabled determination of the ideal reagent concentration, staging configuration, and pH profile in circuits operated with mixbox pH control.
Solvay’ s recent advances in modelling capabilities have allowed the simulation of circuits without direct mixbox pH control. During extraction, the use of preneutralised reagent creates a natural pH drift within the circuit similar to the ideal pH profile attained using mixbox pH control. A similar pH drift occurs in scrub circuits using acidified water as the scrub-feed solution. Modelling has indicated that circuits operated without mixbox pH control can achieve the desired metal separation while simplifying the commercial operation significantly.
Since the active component of CYANEX 272 extractant is a phosphinic acid, metals are extracted through a cation exchange mechanism. Although CYANEX 272 extractant is selective for cobalt in the presence of nickel, a variety of other cations can also be extracted depending on the solution pH. CYANEX 272 extractant is totally miscible with common aromatic and aliphatic diluents, and is extremely stable to both heat and hydrolysis.
CYANEX 272 was reviewed at ALTA 2017, as was Economical precipitation of cobalt and nickel from solution by Glencore Technology’ s Paul Voigt, Mike Hourn and Glenn Stieper.
“ As mine head grades decline and orebodies become more complex,” they explained,“ traditional mineral processing techniques and flowsheets to achieve saleable concentrate from these ores become more difficult. Mines with lower quality concentrates or concentrates with penalty elements are at particular threat. The economics of these operations are far more susceptible to metal price and the availability of other, cleaner concentrates. Additional value may be realised through improved recovery by the inclusion of low grade middling concentrates at the expense of lowering the overall concentrate grade.
“ The most cost effective way to reduce impurity levels is to do so as early as possible in the mining value chain. Established technologies such as fine grinding and fine particle flotation are well established as effective methods in mineral processing unit operations. What is normally overlooked is how a hydrometallurgical process could also be integrated to achieve higher concentrate upgrade at the mill. In the base metals environment, this is mainly because hydrometallurgical processes are associated with production of metal or use of expensive and toxic precipitating agents once the minerals of interest are solubilised. These‘ back-end’ processes can be very expensive particularly with power constraints and the high capital cost associated with low metal tonnes.
“ In response to this, Glencore Technology has developed an alternative method for recovering economic minerals once leached into solution rather than relying on conventional flowsheet options. The method involves the precipitation of base metals in the sulphate system from solution with limestone or lime. The final grade of the precipitate is not usually high enough to attract favourable terms of sale due to dilution from gypsum and sulphate salts. A set of operating conditions have been developed to allow the separation of the base metal precipitate from gypsum by exploiting the difference in particle size, producing a high grade concentrate at low cost. This process was originally developed by Glencore for the application of zinc and copper systems.”
The paper reports on the successful application to nickel and cobalt which had significant advantages over the incumbent precipitation process utilising magnesia.
There are in excess of 400 Mt of accumulated copper slags around the world, with grades ranging from 0.6 % to as high as 1.7 % Cu, as well
Recovering high-tech metals
Solvay’ s CYANEX ® 272 is a phosphinic acid-based SX reagent used commercially to recover and purify cobalt from sulphate solutions. Solvay has
Solvay also offers CYANEX 600 for molybdenum; CYANEX 572 for rare earths; CYANEX 301 for cobalt and nickel co-extraction and CYANEX 921 and 923 for other applications
12 International Mining | JUNE 2017