Mining chemical suppliers can provide both
standard and custom products tailored to
customer needs. (Photo: AkzoNobel)
Chemical Solutions Proliferate
Choosing the right reagent to help process troublesome ores often can result in
significant savings and higher recovery rates, without draining the capex budget
By Russell A. Carter, Managing Editor
Given the cost and production parameters specified in the article—gold ore, 500 tons per hour (t/h) throughput, head grade of 3 g/t and $1,150/oz price—the numbers favor the improved recovery option by far, in terms of speed of payback. It’s a simplistic example, but it illustrates the point. This is an area in which mining chemicals may figuratively be worth their weight in gold—or iron ore or phosphate, potentially enabling producers to tweak or otherwise adjust process-line inputs to obtain small, but valuable improvements in recovery without massive investment.
That isn’t always the case, however; as we’ll see later in the article, the world’s largest gold miner had to spend triple-digit millions to incorporate a new chemical treatment circuit into one of its Nevada operations—but plans to recoup that investment, and more, from recovery of gold in hard-to-process ores that would have required additional capital spending to accomplish by conventional methods.
A flurry of mining-chemical market studies emerged in early 2015, predicting a growth rate of anywhere from 4.8% to 6.5% CAGR through 2020. How those predictions stand up to subsequent economic developments affecting the mining industry during the current slump is anyone’s guess. What is for certain is that mining chemical suppliers often can provide solutions to processing problems that will undoubtedly proliferate as miners are forced to develop lessdesirable, lower-grade deposits in increasingly remote locations.
Tracking the Trends
Against this backdrop of challenge and
opportunity, E&MJ asked Karim Sasioglu,
global marketing manager–mining chemicals
for AkzoNobel Surface Chemistry AB, a major
specialty chemical supplier for the mining
industry, to comment on industry trends.
E&MJ: How can mining chemical suppliers
assist their mineral processing customers
in improving recovery and cutting
costs when faced with the challenges of
lower commodity prices, less money for
equipment upgrades, and lower-grade,
more difficult ores to process?
Sasioglu: As ore grades are depleted, the
utilization and optimization of flotation
becomes even more important. In many
cases, the traditional flotation chemicals
need to be replaced completely or at least
partly by more selective reagents. Most
often, the solution is a compromise. It is
challenging to both improve the selectivity
of the collector to achieve optimal flotation
of complex ores and at the same time
improve flotation kinetics to deal with higher
throughputs. One way to deal with higher
throughputs can be to add a booster to
the reagent to enhance flotation kinetics.
E&MJ: In what ways can mining chemical
suppliers help their mineral processing
customers reduce process water consumption
and/or contribute to less environmental
impact from flotation and other processing
technologies?
Sasioglu: Process water circuits will become
more and more closed. We anticipate the
need for sustainable tailor-made reagents
that can conform to such an environment.
E&MJ: What challenges or benefits do
flotation chemical suppliers encounter as
mineral processors move from smaller,
more numerous flotation machines to fewer,
larger-sized flotation cells? Is there just a
simple linear relationship (i.e., bigger flotation
cells, thus more chemical usage) or are
there hidden factors to consider?
Sasioglu: The reagent dosage is measured by
gram reagent/ton floated ore regardless of
the size or number of the flotation cells. Pulp
density, retention time and flotation kinetics
all determine the size of the flotation cells.
E&MJ: What do you envisage as the
next important near-term steps in the evolution
of flotation technology?
Sasioglu: Flotation technology will continue
to advance to meet the challenges
of more complex ores/lower qualities. We
anticipate the need for sustainable tailormade
reagents to increase. In order to
improve the efficiency and the selectivity
of the flotation reagent through the flotation
circuit, more understanding of the
mineralogy and flotation kinetics is needed.
We anticipate a closer collaboration
between engineering companies, flotation
chemical suppliers and mineral processing
companies for finding the optimal process.
AkzoNobel, along with other major chemical
suppliers, provides both tailor-made and
standard products, and The Netherlandsheadquartered
company prides itself on its
level of customer collaboration and focus on
a sustainable future. For example, the company
said it has extensive knowledge and
experience in assessing the impact of its
flotation collector chemistry within the customer’s
environment, and has developed
unique analysis methods for detecting very
low levels of its products in water and air.
“Choosing the best collector is based on
three basic principles,” Sasioglu explained.
“Each ore is unique; each ore is treated in a
unique process; and the process performance
is optimized with customized collectors.”
AkzoNobel flotation collectors offer optimized solutions for iron ore, phosphate, potash, calcite, and other industrial minerals. The products are recognized under the Armeen, Armac, Armoflote, Atrac, Berol, Ethomeen and Lilaflot trade names.
Chemical Collaborations
There has been a steady stream of notable
developments in the search for methods to
achieve better performance when dealing
with hard-to-process ores and troublesome
concentrates. For example, late last year,
FLSmidth and BASF signed a joint development
agreement to expedite the commercialization
of FLSmidth’s Rapid
Oxidative Leach process targeting difficultto-
process copper concentrates, such as
primary sulphides and concentrates containing
high levels of arsenic.
Under the joint development agreement, BASF will bring additional funding, resources and new novel chemical reagents and processes to more rapidly commercialize FLSmidth’s leaching technology. In particular, BASF said it will incorporate innovative solvent extraction reagents, which exhibit high resistance to degradation and a step change in copper selectivity.
As an example, the two companies pointed out that the decline of copper ore grades in Chile and Peru has driven companies toward new higher-copper-grade ore deposits containing arsenic. This requires costly cleaning, as arsenic is a health and safety risk for copper smelters, which limit arsenic content to a maximum of 0.5% arsenic in the concentrate.
According to BASF, the hydrometallurgical processing of primary copper sulphide concentrates and concentrates containing high levels of arsenic offers an exciting opportunity. “Several years ago, we focused on developing chemicals that would support the industry’ inevitable move towards mine more complex ores, chemicals that required a new leaching technology. We believe that the FLSmidth Rapid Oxidative Leach process combined with BASF’s novel reagents is the game changer that will enable the copper industry to process such ores,” said Christian Lach, vice president– strategic marketing and innovation for water, oilfield and mining solutions at BASF.
In a recent paper2, researchers from FLSmidth described the background and details of the Rapid Oxidative Leach concept as developed by the company, explaining that “…the majority of efforts to improve primary copper sulphide leaching have focused on solution chemistry, temperature, O2 pressure, ultra-fine grinding, the use of catalysts, etc. Historically, very few studies have focused on the solid/solution interface.
“A new, patent-pending approach to catalyzed copper sulphide leaching has been discovered by FLSmidth that enables manipulation of the 2-D semi-conductor properties of chalcopyrite surfaces to the benefit of higher electrochemical reactivity. Copper dissolution rates are then further accelerated by incorporating a Stirred Media Reactor (SMRt) into the process. By using minute amounts of Cu2+ to ‘pre-activate’ chalcopyrite, leach times have been reduced from more than 20 hours with incomplete Cu dissolution to less than 2 hours with 98+% Cu dissolution at 80°C. The pre-activation process takes only minutes to complete at temperatures of 80°C or less.
“The total atmospheric leaching process, incorporating the pre-activation and Stirred Media Reactor, is compatible with existing SX/EW processes.”
Money Well Spent
Also in 2015, Barrick announced that a new
thiosulphate process circuit at its Goldstrike
mine in Nevada had reached commercial
production status in the third quarter, and it
expected full ramp-up of production from the
facility in the first half of this year. The company
developed the concept, which it labeled
as the Total Carbonaceous Matter (TCM)
project, over several years in collaboration
with CSIRO and others to handle large volumes
of double-refractory ore that were not
amenable to Goldstrike’s conventional autoclave
processing methods. Although the
Goldstrike mill also has a roaster circuit for
processing carbonaceous refractory ore,
Barrick would have had to shut down its six
autoclaves after the mine’s single-refractory
ore was depleted, and then probably be
forced to heavily invest in building another
roaster to process additional refractory ore in
order to reach its production targets.
The thiosulphate process now installed at Goldstrike gave Barrick—at a cost of $620 million—a cyanide-free alternative for recovering gold from stockpiled doublerefractory ore that contains an estimated 4 million oz of gold. The company began stockpiling that ore in the early ‘90s.
The use of thiosulphate for this purpose had been a subject of study by Barrick and others for a number of years prior to 2009, at which time Barrick decided to move the concept out of the laboratory and into the demonstration plant stage. Although calcium thiosulphate offers a number of environmental advantages over cyanide in addition to its gold-recovery characteristics, without careful handling it can break down into ineffective chemicals during the resin-in-leach process. Solving that problem, along with developing a roadmap for smoothly transitioning from CIL to thiosulphate/resin leaching took some time, adding to the pressure the company faced in finding a way to keep its autoclave plant open after the amenable ore ran out.
Thiosulphate, under the trade name Thio Gold 300, is manufactured on-site at Goldstrike in a facility designed by Tessenderlo Kerley, a chemical supplier to the mining, agricultural, industrial and water treatment industries.
The capacity of Goldstrike’s TCM facility is just under 14,000 t/d, representing an annual gold recovery figure of 350,000–400,000 oz/y that possibly overshadows the other substantial benefit provided by the TCM project—avoiding a likely loss of money, jobs and production from shutting down its autoclave operation if a successful solution hadn’t been found.
Making More Moly
In another example of how reagents can be
adjusted to target specific objectives, researchers
from Cytec point out in a recent
issue of Cytec’s Solutions magazine3 that
Cu-Mo separation has long been a challenging
process in flotation of porphyry
copper ore. The small amount of molybdenite
(MoS2) in these ores is floated along
with copper to a bulk Cu-Mo concentrate.
The concentrate is then separated by
depressing the copper minerals and floating
MoS2. Sodium hydrosulphide (NaSH)
(or sodium sulphide) is one of the traditional
depressing reagents.
At the Wunugetu mine in China’s Inner Mongolia region, Cu and Mo grades are low and the proportion of secondary copper minerals is high. The porphyry copper ore body has 3 million tons of copper and 600,000 tons of molybdenum reserves, and is the fourth largest copper/molybdenum ore reserve in China. After commissioning in 2009, the mine implemented several technical modifications in the Cu- Mo circuit. In 2010, the mine completed a process optimization project that stabilized the Cu-Mo plant operation.
However, the operation still faced three major challenges: High NaSH consumption (cost), environmental and occupational health concerns associated with the reagent, and logistical arrangements for reagent supply. To solve these problems, the mine set a new target for improvement by searching for a reagent that could provide better dosage-performance, lower toxicity and easier handling.
In 2014, the mine conducted industrial scale trials with a high performance synthetic organic reagent, Cytec’s AERO 8371 PNR, as a copper depressant. The application of AERO 8371 PNR resulted in about 45% reduction in NaSH consumption, and delivered a number of benefits to the mine. NaSH dust and stench were reduced in the reagent warehouse and reagent preparation workshop. Reduction in NaSH consumption resulted in up to a 35% reagent cost saving.
Molybdenum product grade also increased from 45% to 47%, and the copper content in the molybdenum product has decreased from 1.2% to less than 1%, a threshold to allow upgrading the molybdenum product to Class 1 from Class 2. This is achieved with a shorter cleaner circuit, seven-stages vs. nine-stages before the trial.
Furthermore, according to the authors, the stability of the Cu-Mo circuit was improved, resulting in higher Mo recovery. The reduction in NaSH consumption also eased logistics matters and solved certain operational issues. The reduced need for NaSH flakes allowed the mine to purchase the raw material at a higher quality level, which not only benefitted Cu-Mo separation but also helped eliminate blockage of the NaSH solution delivery pipes.