# Advancements in Removing Fluorine from Copper Concentrate

Weiping Liu, Yujie Zhao, Junfeng Chen, Muhammad Azam, David

Asubonteng, Michael Ngoie, Shangyong Lin, Wei Sun

► To cite this version:

Weiping Liu, Yujie Zhao, Junfeng Chen, Muhammad Azam, David Asubonteng, et al. Advance-ments in Removing Fluorine from Copper Concentrate. Mining, Metallurgy & Exploration, 2023,10.1007/s42461-023-04209-424

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<figure><img src="image_1.png" /></figure>
# Advancements in Removing Fluorine from Copper Concentrate

Weiping Liu<fnref n="1" />,<fnref n="2" />,<fnref n="3" /> Ⓓ · Yujie Zhao<fnref n="1" />,<fnref n="2" />,<fnref n="3" /> · Junfeng Chen<fnref n="1" />,<fnref n="2" />,<fnref n="3" /> · Muhammad Azam<fnref n="1" />,<fnref n="2" />,<fnref n="3" /> · David Asubonteng<fnref n="1" />,<fnref n="2" />,<fnref n="3" /> ·

Michael Ngoie<fnref n="1" />,<fnref n="2" />,<fnref n="3" /> · Shangyong Lin<fnref n="1" />,<fnref n="2" />,<fnref n="3" /> · Wei Sun<fnref n="1" />,<fnref n="2" />,<fnref n="3" />

Received: 10 April 2023 / Accepted: 23 July 2023
© Society for Mining, Metallurgy & Exploration Inc. 2023

## Abstract

Copper concentrates are widely used in smelting operations worldwide and typically consist of chalcopyrite (CuFeS₂) as the primary mineral, with chalcocite (Cu₂S) and bornite (Cu₅FeS₄) as secondary copper-bearing minerals. However, these concentrates often contain hazardous impurities, such as the fluorine ion, which can result in various complications during the smelting process. These issues include equipment corrosion, gas treatment requirements, environmental hazards, and strained community relations. Furthermore, high fluorine content in copper concentrates can lead to penalties and limitations during sales. To address these challenges, this comprehensive review assesses current techniques for removing fluorine from copper concentrate. Drawing upon recent research and the findings in the field, the review analyzes the advantages and disadvantages of existing fluorine removal methods and identifies critical issues requiring attention in the future. This review provides valuable insights into the current state of fluorine removal from copper concentrates and serves as a practical guide for researchers and industry professionals in this field.

**Keywords** Copper · Fluorine · Smelter · Flotation · Hydrometallurgical method

## 1 Introduction

Professor Patrick Taylor has had a remarkable career in mineral processing and extractive metallurgy engineering, with significant contributions in the area of flotation technology and extractive metallurgy, including research on copper concentrate. As he retires from his position as Ansell Distinguished Professor of Chemical Engineering at the Colorado School of Mines, it is fitting to honor him for his substantial contributions to the advancement of mineral processing and extractive metallurgy.

Copper concentrate is a vital raw material in numerous industries, owing to copper's exceptional electrical and thermal conductivity. Its usage is widespread and essential in

the production of electronic devices such as wiring, motors, transformers, and other critical components [1]. In the construction industry, it is commonly used in plumbing, roofing, and structural applications. Additionally, the transportation sector relies on copper for vehicle production and infrastructure. The antimicrobial properties of copper also make it useful in healthcare settings [2]. The significance of copper concentrate in modern society is undeniable and its importance is only expected to increase in the future.

Copper concentrate smelting is a crucial process in various industries, but the high concentration of fluorine in the concentrate presents significant challenges. When fluorine reacts with the silica lining of the smelter, it produces a volatile gas that can cause equipment damage and harm workers [3]. Moreover, the discharge of high levels of fluorine from copper smelters can cause health and environmental problems [4]. Therefore, the removal of fluorine ions from copper concentrate is critical, and thus, the current status of fluorine ion removal from copper concentrate will be reviewed in this paper.

### 1.1 Copper Concentrate with Excess Fluorine Ion

Copper is widely used in the appliance and construction industries, and thus, the copper price is highly related to

<figure><img src="image_2.png" /></figure>

<footnote>Weiping Liu
wliu.met@outlook.com</footnote>

<footnote n="1">¹ School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China</footnote>

<footnote n="2">² Hunan International Joint Research Center for Efficient and Clean Utilization of Critical Metal Mineral Resources, Central South University, Changsha 410083, China</footnote>

<footnote n="3">³ Key Laboratory of Hunan Province for Clean and Efficient Utilization of Strategic Calcium-containing Mineral Resource, Center South University, Changsha 410083, China</footnote>
the global economy. The world's largest producers and consumers are Chile and China respectively [5]. The copper was recovered from sulfide copper concentrate mainly by roasting and smelting [6]. About 70% of copper is produced from sulfide copper concentrate, which mainly contains chalcopyrite mineral (CuFeS₂) and the minor percentage is the secondary copper minerals, such as chalcocite (Cu₂S), bornite (Cu₅FeS₄), and covellite (CuS) [7–9].

The copper concentrate contains copper, iron, sulfur, and also some other harmful elements such as fluorine ions [10]. The smelting process involves the removal of unwanted impurities such as iron, sulfur, and gangue materials before or during the process to the greatest extent possible. However, the halogen elements, particularly fluorine, pose a significant challenge as they are difficult to eliminate during the process and can cause severe issues for both the smelter and mine sites [11, 12]. Fluorine in the copper concentrate and acid solutions from smelting combines to create a highly corrosive H₂SO₄-HCl-HF acid brine mixture. This mixture accelerates the corrosion of smelting equipment, acid-resistant tiles, fiberglass pipes, packing, and SiO₂ catalyzer substrates, necessitating neutralization [13]. In addition, industrial wastewater containing high levels of fluorine ions can have adverse effects on the ecosystem and lead to strained relationships with local communities.

Copper smelters are predominantly situated in China, Japan, and Europe [14]. In case the copper concentrate contains impurity elements beyond the stipulated limits, the smelters charge financial penalties. Fluorine is a particularly significant concern due to its potential impact on the environment and local communities. As a result, Chinese customs regulations stipulate that the mass percentage of fluorine ions in imported copper concentrate must be below 0.1% to enter the largest copper concentrate market in the world in Table 1 [15]. In Japan, a financial penalty of $1.0 per 0.01% above 0.033% is imposed by copper smelters. The financial penalty of $1.5 per 0.01% above 0.030% fluorine penalty limit is applied in Europe smelter [16]. In Australia, the financial penalty of $1.0 per 0.01% above 0.015% is imposed by copper smelters [17]. The negotiated price for the sale of copper concentrate can be significantly impacted by penalties for impurities. Several factors determine the price of copper concentrate, including the market price for London Metal Exchange (LME) Grade

A copper cathode, payable copper content in the concentrate, credits for valuable metals in the concentrate other than copper, treatment and refining charges, and deductions for penalty elements. The payable copper content varies with the copper grade and is typically 95-97% for copper grades between 20 and 30% [14]. Treatment and refining charges reflect the costs involved in smelting and refining, which are around $85.10 per dry metric ton and $0.0851 per payable copper pound respectively [18]. For a copper concentrate with 28% grade, refining costs are approximately $50 per dry metric ton.

As of April 2023, the London Metal Exchange reported that the average market price for Grade A copper cathode is $8,800 per metric ton [19]. Based on this, copper concentrate with a copper grade of 28% is estimated to sell for around $2,200 per metric ton. It is important to note that this estimate doesn't include deductions for payable metals, credits, and penalties. Penalties can significantly reduce the value of copper concentrate. For instance, in this paper, the fluorine penalty deduction ranges from $7 to $54 for copper concentrate containing 0.1 to 0.57% fluorine ion, accounting for 0.3 to 2.4% of the net value of the concentrate before the penalty element deduction. The deduction rate due to fluorine ion is expected to increase as the LME copper price decreases.

Fluorine impurities in copper concentrates pose economic and environmental issues in smelting operations. Neutralizing these impurities requires expensive procedures that can be avoided by removing the fluorine before smelting. This results in a more efficient and sustainable process as the number of harmful ions introduced to the smelter is reduced [7, 8]. Hence, there is a strong motivation for mine sites to remove fluorine elements from copper concentrates to avoid penalties or losing market share. Meanwhile, the smelters in China also process the local copper concentrates. The local copper concentrates from different small mine sites have fluorine mass percentages much higher than 0.1% with different mineralogical compositions. It is a challenge to reduce the fluorine ion content at each mine site due to the variance in mineralogical and the limited research ability or financial investment at local small mining companies. In this regard, the smelter received the local high fluorine copper concentrates with varying mineralogy also looking for an economical and general method to reduce the fluorine ion before the smelting. Overall, there is an urgent need and motivation for copper smelter companies, and mining companies in China and abroad to remove fluorine from copper concentrate.

## 1.2 Fluorine Removal Progress in Copper Concentrate

The strategies currently utilized to manage high fluorine copper concentrate are diverse and vary between smelters and mining companies. Custom smelters that purchase copper concentrate for smelting and refining generally blend concentrates with

<table><caption>**Table 1** Copper concentrate maximum fluorine level and approximate penalty</caption><thead><tr><th></th><th>Fluorine penalty limit, %</th><th>Penalty</th><th>Reference</th></tr></thead><tbody><tr><td>China</td><td>0.1</td><td></td><td>[15]</td></tr><tr><td>Japan</td><td>0.033</td><td>$1.0 per 0.01% above 0.033%</td><td>[12]</td></tr><tr><td>Europe</td><td>0.030</td><td>$1.5 per 0.01% above 0.030%</td><td>[16]</td></tr><tr><td>Australia</td><td>0.015</td><td>$1.0 per 0.01% above 0.015%</td><td>[17]</td></tr></tbody></table>
different fluorine levels to obtain a smelter feed that has an average fluorine ion level of less than 0.1%. Another approach involves modifying sulfuric acid plants to handle copper concentrates with high fluorine levels, which may include constructing a new smelter or altering an existing third-party smelter [4].

Copper concentrates with more than 0.1% fluorine ion are typically challenging to sell [4]. Mining companies use primarily flotation and hydrometallurgical leaching techniques to remove fluorine ions from copper concentrate and produce a “clean” product without market restrictions. Fluorine-bearing minerals can be suppressed during flotation, but the association or encapsulation of fluorine minerals with copper sulfides leads to significant losses of copper or gold. The hydrometallurgical process was able to reduce the fluorine level in a chalcocite/bornite concentrate from 0.22 to 0.02%, although some copper and other elements were also leached out. The flotation and hydrometallurgical methods vary depending on the specific mineralogical composition. The hydrometallurgical process, moreover, necessitates significant changes in capital and operations to the current flotation plant and subsequent product line, restricting its application in mining industry.

Fluorine removal is crucial for penalty-free copper concentrate sales and sustainable smelting. While existing techniques remove fluorine, sacrificing valuable metals remains an issue. The following session explores typical fluorine removal methods and highlights key considerations for developing novel technology to process high fluorine copper concentrate.

## 2 Fluorine Removal Techniques

The efficient removal of fluorine from copper flotation processes is a significant metallurgical challenge due to the unique mineralogical characteristics of each ore and the specific objectives of each mine. There is no single universally applicable approach for dealing with high fluorine copper concentrate; rather, methods vary depending on the mineralogical composition of the concentrate and the overall goals of the mine. Smelters that receive high fluorine copper concentrate with varying mineralogical compositions from different mines seek a general, cost-effective method for reducing the fluorine ion. This session will review typical methods for dealing with high fluorine copper concentrate, including fluorine removal applications in smelting, froth flotation, and hydrometallurgical leaching.

### 2.1 Fluorine Removal in Smelter

Fluorine may be present in copper concentrate as an impurity, depending on the initial fluorine content of the ore and its

mineralogical characteristics. High levels of fluorine can negatively affect the smelting process by causing equipment malfunctions and contaminating the surrounding environments. Hence, to ensure optimal performance and environmental sustainability, the fluorine content in copper concentrate must not exceed 0.1%.

In copper smelting operations, the presence of fluorine in concentrates poses significant challenges to attached sulfuric acid plants. The fluorine ion can corrode acid-proof tiles, fiberglass pipes, packing materials, and SiO₂-containing catalyzer substrates, as well as cause damage to cast iron pipes to a lesser extent. Upon entering the flash smelter, a small portion of the fluorine in copper concentrate becomes slag in the form of silicon tetrafluoride. The resulting dry slag is cooled with water and sent to a smelting slag plant. Upon contact with water, the silicon tetrafluoride reacts to form hydrofluoric acid, as described by Equation (1) [4].

$$ \mathrm{SiF}_{4}+\left(\mathrm{X}+2\right) \mathrm{H}_{2} \mathrm{O}=\mathrm{SiO}_{2} \cdot \mathrm{XH}_{2} \mathrm{O}+4 \mathrm{HF} \quad (1) $$

As a gas, fluorine is released from the slag and has little impact on the cooling equipment or environment due to its small concentration. During the copper concentrate production process, most of the fluorine becomes hydrofluoric acid in the furnace gas. This acid is collected and sent to a sulfuric acid plant where it poses a serious threat to the equipment and processes involved. The impact of the fluorine ion can be described as follows:

* The fluorine ion causes corrosion of the equipment used in the sulfuric acid purification system. The materials used in this equipment, such as fiber-reinforced plastics (FRP) or Hastelloy, are particularly vulnerable to damage from high levels of fluorine ions. The gas cooling tower and demister can also be corroded by high fluorine ion circulating solution. The erosion of the FRP layer by gas and waste acid can lead to a reduction in pressure resistance, which can damage the equipment at high pressure.

* The activity of the catalytic converter is limited by the fluorine ion. In the sulfuric acid plant, three basic systems are used: gas washing and purification; SO₂ catalytic converter; and acid system. During the conversion process, the sulfur dioxide reacts to generate sulfur trioxide through the catalytic action of vanadium pentoxide. However, the fluorine ion can destroy the silicon compound catalytic substrate, causing damage to the converter.

* The fluorine ion erodes the tile in the drying tower and adsorption tower. The tile, demister, and filler in the drying tower can be severely eroded by gas with high fluorine content. This erosion can have a significant impact on the entire system since the tile in the tower cannot be repaired.

* The presence of fluorine ions in wastewater can negatively impact the system's performance. To neutralize
these ions, an aluminum sulfate reagent can be added. However, if the concentration of fluorine ions is too high, it can damage equipment and ORP electrodes. This damage reduces the ORP electrode's lifespan and limits its ability to measure copper and arsenic in waste acid. Additionally, high levels of fluorine in waste acid can accelerate erosion in pressure filters and centrifuges.

To address the problems caused by fluorine ions, smelters implement several measures to reduce the impact on the sulfuric acid plant:

* Copper concentrate is classified and piled up based on its fluorine ion concentration. The frequency of assaying the copper concentrate is increased to ensure proper sorting.

* Blending strategies are used to mix copper concentrate with different fluorine ion concentrations, ensuring that the average fluorine content is below 0.1%.

* Gas purification systems include fluorine removal equipment to reduce the erosion of sulfuric acid production equipment.

* Aluminum sulfate is used to neutralize the fluorine ion in waste acid.

Despite their efficacy in mitigating the adverse effects of fluorine ions, the aforementioned measures often entail substantial capital and operational costs for smelters. The cost of frequent fluorine ion assay, blending, and upgrading the sulfuric acid plant system to cope with high fluorine content in copper concentrate cannot be ignored. Given the pressing need for a green and low-carbon circular economic development, smelters have been incentivized to pass the costs of fluorine removal as a penalty to mining companies. Moreover, there is a urgent need to develop an economical and eco-friendly general method to reduce the fluorine ion levels in high fluorine copper concentrate sourced from local small copper mines. Efforts in this direction could prove valuable in establishing an environmentally sustainable mining and smelting industry.

## 2.2 Flotation Approach

Froth flotation separates valuable minerals from gangue minerals by exploiting wettability differences through functionalized reagents. It produces concentrate and tail streams and is widely used for various minerals, including metal sulfides, oxides/silicates, industrial minerals, and coal. Froth flotation is an essential mineral processing technique that plays a crucial role in the production of important metals and industrial minerals.

Fluorine concentration exceeding 0.1% in copper concentrate leads to significant financial penalties imposed by smelters. Froth flotation can remove fluorine ions, but its effectiveness depends on ore characteristics and mining objectives. The success of this approach relies on understanding interactions between reagents, mineralogy, and operating conditions. Suitable collectors, modifiers, depresnts, pH, pulp density, and water adjustments are critical for the optimal separation of fluorine-containing minerals [20, 21]. This session will discuss the direct and reverse flotation techniques used for fluorine removal.

### 2.2.1 Direct Flotation

In direct flotation, the valuable mineral is recovered as a concentrate while the gangue minerals containing fluorine ions are suppressed and sent to the tail during this process.

The Ok Tedi copper-gold deposit in Papua New Guinea consists of porphyritic intrusive rocks, with chalcopyrite as the primary copper mineral and bornite and chalcocite as secondary copper minerals. The copper concentrates contain fluorine ions which are predominantly found in talc and phlogopite. Talc is the main contributor to the fluorine content with an overwhelming proportion (64%) due to its high percentage and fluorine content per unit. Talc has a natural hydrophobicity that makes it easily float; thus, it is relatively more concentrated in the copper concentrate. Phlogopite accounts for 22% of the fluorine content and is present in all ore types including skarn and intrusive rocks. The dominant flotation mechanism for talc and other fluoro-silicate minerals is entrainment. However, some talcs exhibit poor natural hydrophobicity which makes them susceptible to floating [22, 23]. In the Ok Tedi mine, the majority of the fluorine was among the scavenger concentrate, with up to 40% present in the fraction less than 12.7 microns, indicating its presence in slow-floating and fine minerals. As shown in Fig. 1, to decrease the fluorine content in the concentrate, carboxyl methyl cellulose (CMC) is commonly used as an organic depressant, reducing it to a range of 0.04-0.09% F. The use of CMC can effectively decrease the fluorine content in the concentrate, but its potential to depress chalcopyrite is a drawback that needs to be considered [23].

The Prominent Hill mine in South Australia contains chalcocite, bornite, and chalcopyrite as the main copper-bearing minerals [24]. The fluorine level in the copper concentrate is highly variable and can reach up to 0.57% F ion. Fluorine is primarily associated with minerals such as fluorite, sericite, apatite, bastnaesite, and florencite. To decrease the fluorine content in the copper concentrate, regrinding the concentrate to less than 20 µm using an IsaMill™ and increasing the additional flotation cleaning capacity with the Jameson Cell were employed. This process aimed to liberate the fluorine-bearing minerals associated with the
<figure><img src="image_3.png" /><figcaption>**Fig. 1** The flowsheet in the flotation of Ok Tedi Fluorine Bearing Minerals, Papua New Guinea</figcaption></figure>

valuable copper sulfides. Subsequently, intensive froth washing and multiple stages of cleaning were utilized, which finally reduced the fluorine level to less than 0.07% (Fig. 2). The additional regrinding and cleaning capacity required to achieve this improvement in copper and gold grade was justified, despite the potential for fluorine entrainment [22]. A similar strategy, involving additional regrinding, several stages of cleaning, and lower solid density, was also used successfully in copper mines with chalcocite as the primary copper mineral, which approach reduced the fluorine level from 0.19 to 0.06% [25].

The Alemão mine, located in the Carajás region of Pará state, Brazil, is an iron oxide-hosted copper-gold deposit owned by Companhia Vale do Rio Doce (CVRD). Fluorine is present in several minerals at Alemão, including fluorapatite, biotite, chlorite, fluorite, allanite, monazite, and amphiboles. Bench scale flotation tests were carried out on the deposits, resulting in the production of a copper concentrate containing 0.11–0.27% F and 20% Cu. However, the fluorine level in the Alemao ore was reduced to 0.02–0.03% by regrinding it to a particle size of 70% less than –16 µm and using a hexametaphosphate depressant during the cleaning stage [26] (Fig. 3).

The sulfide copper ore plant located in Anhui, China, produces copper concentrate products with 18.20% Cu, 0.25% F, and 9.26% MgO. The copper grade is low, and the fluorine and magnesium content exceed the smelting

plant's requirements (i.e., F content < 0.1%, MgO content < 5%). The copper concentrate contains fine particles of talc, serpentine, and chlorite, which tend to muddy and float minerals containing F and MgO. These minerals are the main cause of excessive fluorine and magnesium content in the copper concentrate. To tackle this problem, the gangue minerals containing F and MgO were depressed using DG11, which was developed by the Guangdong Institute of Resources Comprehensive Utilization in China. The process involved one roughing, one cleaning, one scavenging, and middling returning in a proper order into the flow. As a result, the copper concentrate achieved a grade of 25.11% and a recovery rate of 97.45%, including only 0.08% F and 2.02% MgO. This process not only improved the copper concentrate's grade but also significantly reduced the fluorine and magnesium content, meeting the copper smelting plant's requirements [27] (Fig. 4).

As for the fundamental flotation chemistry of fluorine-carrying minerals, the attachment of bubbles to talc and phlogopite surfaces in the presence of polysaccharides was analyzed by the contact angle, water film thickness measurements, and bubble attachment time. The results showed that the talc surface was hydrophobic and its contact angle is 80°, while the phlogopite surface was hydrophilic, with a contact angle of zero [28]. The presence of polysaccharides affected the stability of bubble attachment and water film at the talc surface. With the increasing concentration of polysaccharides, the contact angle decreased slightly, and the bubble attachment time increased significantly. In some cases, the increase in bubble attachment time was as high as 1000-fold, as observed with guar gum and starch. The talc surface changed from a hydrophobic state to a hydrophilic state with high concentrations of polysaccharides, and thus, the water film became stable, preventing bubble attachment. Guar gum was more effective to alter the talc surface hydrophobicity compared to starch and dextrin [29].

In the copper industry, fluorine often ends up in the copper concentrate due to several factors such as poor liberation, association with non-sulfide minerals that naturally float, and entrainment. As shown in Table 2, the fluorine ion is

<figure><img src="image_4.png" /><figcaption>**Fig. 2** Regrind and cleaner flowsheet in Prominent Hill Mine, Australia</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>**Fig. 3** Regrind and cleaner flowsheet in Alemão mine, Brazil</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>Fig. 4 The flowsheet in sulfide copper mine, Anhui, China</figcaption></figure>

mainly associated with copper sulfide minerals, particularly chalcopyrite, as well as non-sulfide minerals such as talc, phlogopite, serpentine, and chlorite. To address this issue and reduce the fluorine content in the copper concentrate, it is necessary to implement regrinding and additional cleaner capacity with selective depressants. However, it is important to consider the potential loss of valuable metals caused by the use of depressants when conducting an economic analysis.

### 2.2.2 Reverse Flotation

Reverse flotation separates gangue minerals from valuable minerals by floating the gangue minerals as concentrate and depressing the valuable minerals as tailings.

The large-scale copper-molybdenum mine project located in the Andes of South America is a porphyry copper mine with a capacity of ten million tons. The copper concentrate extracted from the mine contains 0.14% fluorine ion, which is predominantly associated with talc and mica. Talc is the primary mineral carrying fluorine, accounting for 25% of the copper concentrate, while mica only makes up 2%. To exploit the natural hydrophobicity of talc, the reverse flotation process was used, as illustrated in Fig. 5. NaHS was employed to depress chalcopyrite in a nitrogen atmosphere, with the chalcopyrite reporting to the tailings as the final copper concentrate, whereas the fluorine ion-bearing

minerals and other hydrophobic minerals floated as concentrate. Under the experimental conditions of 35% solids, feed P80 of -200 mesh, -500mV, 5.6 kg/ton NaHS, and N₂ gas atmosphere, the removal rates of MgO and fluorine in the copper concentrate were 79% and 59%, respectively. This resulted in a 0.5% decrease in Cu recovery, but the copper concentrate grade increased from 19.0 to 21.3%. Despite the improvement in copper concentrate grade, the copper loss remains an issue, and the mine site needs to strike a balance between copper loss and the penalty for fluorine [30].

The Ok Tedi copper and gold deposit is situated in the North Fly district of Western Province, Papua New Guinea. To prevent the loss of valuable sulfides carrying copper and gold, sodium hydrosulfide (NaHS) was used to lower the pulp oxygen levels in the Jameson cell. This lowered the electrochemical potential under the value of 360 mV (SHE) in the high pH range (11, 12) during a single batch of reverse flotation. However, the fluorine content in the copper concentrate remained above 0.19%. To address this issue, a two-stage Jameson Cell closed flowsheet was employed, as illustrated in Fig. 6. This resulted in a 45% reduction in the fluorine ion level to around 0.1% in copper concentrate and a 2% improvement in the copper grade[31].

Copper flotation plants that process fluorine-containing copper ores often adjust their flowsheets based on the ore mineralogy to minimize fluorine recovery. As shown in Table 3, when talc is the primary fluorine-carrying

<figure><img src="image_7.png" /><figcaption>Fig. 5 Fluorine removal by reverse flotation</figcaption></figure>

<table><caption>**Table 2** The summary of fluorine depression in direct flotation</caption><thead><tr><th>Mine sites</th><th>Main fluorine carrying mineral</th><th>Grinding size</th><th>Depressant</th><th>Initial fluorine% in feed%</th><th>Final fluorine%</th><th>Cu loss%</th><th>Reference</th></tr></thead><tbody><tr><td>Ok Tedi mine</td><td>Talc, phlogopite</td><td>&lt; 170 µm</td><td>CMC(carboxy methyl cellulose)</td><td>0.10-0.51%</td><td>0.04-0.09%</td><td>-</td><td>[22]</td></tr><tr><td>Prominent Hill mine</td><td>Fluorite, sericite</td><td>P80=23 µm</td><td>-</td><td>0.10-0.57%</td><td>0.07%</td><td>-</td><td>[24]</td></tr><tr><td>Alemao mine</td><td>Fluorapatite, biotite, chlorite, fluorite, allanite</td><td>P70=16 µm</td><td>Hexametaphosphate</td><td>-</td><td>0.02-0.03%</td><td>-</td><td>[26]</td></tr><tr><td>A copper mine in Anhui, China</td><td>Talc, serpentine, and chlorite</td><td>-</td><td>DG11</td><td>0.25%</td><td>0.08%</td><td>-</td><td>[27]</td></tr></tbody></table>
mineral, which naturally exhibits hydrophobicity, reverse flotation can be applied to separate talc by depressing copper sulfide minerals. In the case of the Ok Tedi mine, additional cleaner capacity has proven helpful in reducing fluorine removal efficiency. However, it should be noted that copper loss is still a concern in reverse flotation, as it is in direct flotation. Thus, the mine site must balance the loss of valuable metals with the penalty for the presence of fluorine ions in the copper concentrate.

### 2.2.3 Copper Loss and Fluorine Penalty Economic Analysis

The design of a flotation flowsheet to remove fluorine from copper concentrates is a challenging task that requires consideration of several factors, such as the surface properties of fluorine-carrying minerals, their liberation, and their association with copper sulfide minerals. Both direct and reverse flotation methods have been developed to address this issue, but both have their drawbacks, mainly the balance between copper loss and the fluorine penalty. To determine the feasibility of current flotation techniques for removing fluorine from copper concentrates, an economic analysis model was developed. This model considered only copper as a valuable mineral, ignoring gold, silver, or molybdenum. The economic analysis was based on the market price of copper and aimed to determine the optimal balance between the fluorine penalty and copper loss.

The cash flow analysis was conducted considering a mine with a daily throughput of 100,000 tons having a

0.40% copper grade. The concentrate copper grade was assumed to be 18% with 85% copper recovery, and the payable copper factor was set at 96.5%. The TC/RC was estimated to be $85.1/8.51¢, respectively. Copper recovery losses were assumed to be 2% and 0.5% for direct and reverse flotation, respectively. The direct flotation method showed a decrease in fluorine concentration from 0.25 to 0.08% with the depressant, whereas the reverse flotation technique showed a decrease in fluorine concentration in the concentrate from 0.07 to 0.03%. The cash flow loss is a combination of copper loss and fluorine penalty, and it increases with increasing copper prices, as demonstrated in Fig. 7. The deduction of copper recovery in the flotation process, as a result of depression, is closely related to the reduction in cash flow. As expected, the reverse flotation technique, which has a copper recovery loss of 0.5%, results in a lower cash flow loss compared to direct flotation, which has a copper loss of 2%. It is important to note that this simplified calculation did not include the price of precious metals, transportation fees, and taxes. The economic analysis further emphasized that the loss of valuable metals during the removal of fluorine by flotation should be carefully considered during decision-making processes at mine sites.

## 2.3 Hydrometallurgical Leaching

Flotation is a widely used process to produce copper concentrate; however, separating fluorine-bearing minerals from copper minerals presents a challenge. This difficulty arises because fluorine-bearing minerals are frequently associated with or enclosed within copper sulfides, making separation solely through flotation unattainable. To address this challenge, hydrometallurgical leaching has been introduced as a solution.

To selectively extract fluorine from metal ore concentrates, a leaching process with sulfuric acid ($H_2SO_4$) and aluminum sulfate ($Al_2(SO_4)_3$) is commonly used as shown in equation (2) [32]. The main fluorine species in the leaching process include two soluble species of $AlF^{2+}$ and $AlF_2^+$, and several species of $AlF_3$, $AlF_4^-$, $AlF_5$[2], and $AlF_6$[3], which are either insoluble or partially soluble [6]. Leaching is conducted at atmospheric pressure and temperatures around 60°C, with sulfuric acid regulating the pH between 3.0 and 4.3 for the extraction of fluorine ion [6, 22]. If the

<figure><img src="image_8.png" /><figcaption>**Fig. 6** Reverse flotation to reject fluorine at OK Tedi Copper/Gold concentrator</figcaption></figure>

<table><caption>**Table 3** The summary of fluorine depression in reverse flotation</caption><thead><tr><th>Mine sites</th><th>Main fluorine carrying mineral</th><th>Depressant</th><th>Initial fluorine% in feed</th><th>Final fluorine%</th><th>Cu loss%</th><th>Reference</th></tr></thead><tbody><tr><td>Porphyry copper mine</td><td>Talc, mica</td><td>NaHS</td><td>-</td><td>0.03%</td><td>0.5%</td><td>[24]</td></tr><tr><td>Ok Tedi</td><td>Talc, phlogopite</td><td>NaHS</td><td>0.10-0.51%</td><td>0.10%</td><td>-</td><td>[31]</td></tr></tbody></table>
<figure><img src="image_9.png" /><figcaption>Fig. 7 Cash flow analysis</figcaption></figure>

pH is below 3.0, hydrogen ions can compete with Al³⁺ ions to react with fluorine ions, limiting the availability of fluorine ions to react with Al³⁺ ions and reducing the extraction rate of fluorine ions from the concentrate [22]. If the pH is above 4.3, the availability of aluminum ions is limited due to aluminum hydroxide precipitation from solution [6].

$$ \text{mineral} - F + \text{Al}^{3+} = \text{mineral} + (\text{AlF})^{n\pm} \quad (2) $$

where n is an integer.

Olympic Dam mine belonging to BHP Billiton in South Australia employs a process that uses dilute sulfuric acid to extract fluorine ions from copper concentrate [6]. The ore deposit contains fluorine ions in the range of 1–2 wt%, with fluorite being the primary source [33]. Under experimental conditions of a 24-h leaching time, a temperature range of 30–60°C, and an initial sulfuric acid concentration between 40 and 98 g·L⁻¹, approximately 90% of fluorine ions were extracted. However, at a lower initial sulfuric acid concentration of 9.8 g·L⁻¹, the extent of fluorine ion extraction decreased to approximately 15–20%. It is important to note that using a dilute sulfuric acid with a concentration of less than 98 g·L⁻¹ resulted in only a limited amount of copper being leached from the concentrate [12].

To address the presence of association or encapsulated fluorine ion-carrying minerals in copper sulfides, the CVRD Technology Center, now known as Vale, has developed a leaching technique coupled with solvent extraction-electrowinning (SE-EW) technology to produce high-quality copper concentrate for copper smelters. The copper-fluorine concentrate is treated with acids such as H₂SO₄ or HCl at a controlled temperature, acid-to-concentrate ratio, and residence time as shown in Fig. 8. This method ensures efficient extraction of copper while controlling the amount of fluorine in the final product [34]. The acid attacks and alters the lattice structure of fluorine-bearing minerals, converting them into amorphous compounds and releasing the fluorine ion. Depending on the type of copper ore, copper and other

<figure><img src="image_10.png" /><figcaption>Fig. 8 Fluorine removal by CVRD flotation and solvent-electrowinning technique</figcaption></figure>

ions may also be leached along with the fluorine ion, necessitating SE-EW to recover copper from the mother liquor. This method is effective for the leaching of chalcocite and bornite mineralization but yields limited copper dissolution for chalcopyrite mineralization [34]. For chalcocite/bornite concentrate, containing approximately 0.21% fluorine ion, 60% of fluorine was leached by adding 23 kg of 97.5 wt% H₂SO₄ per ton of concentrate with a pH of (3.5 ± 0.2); this concentrate was composed mainly of fluorite (93%). In contrast, for chalcopyrite concentrate containing approximately 0.06% fluorine ion, composed of 72% fluorite and 24% apatite, only around 10% of fluorine was extracted by adding 9 kg of 97.5 wt% H₂SO₄ per ton of concentrate with a pH of (3.5±0.2). The low fluorine leaching efficiency for chalcopyrite concentrate can be attributed to the low initial fluorine concentration and limited mineral liberation [35]. To enhance fluorine extraction, aluminum sulfate can be added to the leaching process. The copper yield from chalcocite/bornite concentrate was significantly higher (~4.5% of total Cu) than from chalcopyrite concentrate (~0.3% of total Cu). To recover the copper, it was cemented with powder Fe and treated with liquor by raising the pH to 9.0 using calcium hydroxide pulp.

In hydrometallurgical processes, fluorite and apatite are the primary mineral sources of fluorine, but the specific minerals containing fluorine can vary depending on the mine's mineralogy. These minerals may include talc, mica, phlogopite, sericite, fluorapatite, biotite, chlorite, allanite, and serpentine. The appropriate leaching conditions, such as the leaching reagent, time, and temperature, depend on the concentration and mineral speciation of fluorine in the copper concentrate. In addition to copper, fluorine is also a concern in other metal concentrates like zinc and lead, and studying the leaching behavior of fluorine-bearing minerals in these concentrates can provide insights into the treatment
of high-fluorine copper concentrate with diverse mineral compositions.

At South32's Cannington mine in Queensland, aluminum sulfate was used to acid leach zinc and lead concentrates to remove fluorine ion [11]. The fluorine ion in the zinc and lead concentrate was mainly associated with apatite, fluorite, and silicate minerals such as talc, ferropyrosmalite, and chlorite. Analysis of the leach residue shows that the majority of the residual fluorine ion was associated with talc and ferropyrosmalite, while a minor amount was associated with chlorite. Notably, the fluorine ion associated with apatite and fluorite was almost entirely leached, while that associated with silicate minerals like talc, ferropyrosmalite, and chlorite was partially or completely insoluble in the acid and aluminum sulfate leaching system. The presence of fluorine in silicate minerals is due to varying degrees of substitution of hydroxyl groups (-OH) with fluorine (-F) [11]. Talc possesses a platy particle morphology and a 2:1 layer structure, with oxygen atoms present on the layer surfaces, resulting in its hydrophobic properties. This hydrophobic nature is believed to be the underlying reason for the slow leaching behavior of talc [36]. Okada et al. [37] highlighted the significant impact of AlO₄ substitution in the SiO₄ tetrahedral sheets of the silicate layer on the leaching rate of various minerals. Due to its absence of Al substitution in the SiO₄ tetrahedral sheets and its classification as a non-swelling clay mineral, talc exhibits a very slow rate of acid leaching. This is attributed to the higher acid resistance of SiO₂. Consequently, the leached products derived from talc are characterized as nonporous [38]. However, when subjected to mechanical treatment, the surface and layer structure of talc undergo changes, significantly enhancing acid leaching compared to unground talc in the depletion of magnesium (Mg) ions [36]. This observation further supports the notion that talc's layered structure and inherent hydrophobicity may contribute to its insolubility in acid and aluminum sulfate leaching systems.

The practicality of utilizing a wet metallurgical leaching process for commercial production relies not only on how much metal can be extracted but also on several other factors. These factors include the limitations on fluorine ions, the accessibility and cost of leaching agents, and the financial viability of retrieving valuable elements from the leachate. Compared to flotation, the hydrometallurgical fluorine removal process has the advantage of producing a fraction of the copper (specifically for concentrate with leachable copper) as cathode and upgrading the copper concentrate, turning a low-value or high-commercialization-risk product into two high-value products. As we discussed before, the leaching reagent or system may be varying based on the mineralogical composition, especially the fluorine ion-bearing minerals. The systematic leaching analysis of the fluorine-bearing minerals is necessary and its feasibility of

application in copper concentrate with varying mineralogical compositions from different mines is in urgent need. However, hydrometallurgical leaching made a significant change to the present plant flowsheet, its economical feasibility may vary according to the mine site situations.

## 3 Discussion and Conclusion

High levels of fluorine in copper concentrates can result in significant penalties for copper smelters, making it imperative for mines to find effective methods to remove it. This challenge is particularly acute for China smelters, which also deal with local concentrates that have high fluorine content. Feed blending is a common method used to control fluorine concentration in copper concentrates, but the costs of frequent fluorine ion assay, blending, and upgrading sulfuric acid plant systems cannot be overlooked. Direct flotation, which involves depressing fluorine-carrying minerals, is another option for reducing fluorine content. Reverse flotation can also be used to float hydrophobic talc, a mineral that often carries fluorine, by depressing copper sulfide minerals with NaHS. However, both direct and reverse flotation may result in copper losses due to the association of fluorine-carrying minerals with copper sulfide minerals, or the impact of depressants on copper minerals. Grinding and additional cleaner capacity have also been shown to be effective in reducing fluorine content due to entrainment. Ultimately, a balance between the fluorine penalty and copper loss must be struck based on the copper price at the mine site.

Hydrometallurgical routes have been reported as effective for removing fluorine and upgrading the copper grade. Current reports mainly focus on leaching copper concentrate with fluorite and apatite as the main fluorine-carrying minerals. More analysis is needed to determine the feasibility of leaching fluorine-bearing minerals from copper concentrate with different mineralogical compositions from various mines.

High levels of fluorine in copper concentrate have been reported in several copper mines across the world, including Papua New Guinea, South Australia, Brazil, China, and South America. Many other copper mines are also facing similar challenges recently. For instance, PTFI, one of the world's largest copper and gold mining companies located in Indonesia, has also reported a high fluorine problem. Fluorine is found in higher levels in certain types of ores, such as DMLZ, GBC, and KL-low pyrite ores, which are extracted from the mine [39]. The reported and forthcoming fluorine problems in copper mines require further effort to address the shortcomings of current smelter and mine site practices. More importantly, new technologies are needed to mitigate copper loss issues. Current research
in this area is limited, and additional studies are necessary to develop effective solutions.

**Funding** This research received financial support from the Central South University Startup Fund and the National Key Research and Development Program of China (No. 2022YFC2905104).

**Declarations**

**Competing Interests** The authors declare no competing interests.

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