Alkaline gelatinised cassia tora and locust bean gums as talc depressants: Adsorption and thermochemical aspect

doi:10.21203/rs.3.rs-3327563/v1

Talc is a gangue mineral of most platinum group metals and base metals ores commonly found in the Southern African mineral repository. It is naturally hydrophobic, and invariably, the depression of talc is paramount and challenging in the flotation of these ores. This paper introduced cassia tora gum (CTG) and locust bean gum (LBG) as novel talc depressants. The adsorption densities, thermochemical, and talc depression of these depressants were studied using adsorption, zeta potential and microflotation studies. Talc flotability in the absence of the depressant was 89% this implied that the talc used in this study was naturally floatable. The adsorption studies revealed that CTG yielded the highest talc adsorption density, followed by LBG and CMC, and their adsorption densities were 5.8 mg/m2, 4.6 mg/m2 and 3.5 mg/m2, respectively. PGM flotation occurs at pH 9. Therefore, the zeta potential results at this pH were given more focus in the present study. The zeta potential values at pH 9 were -5.75 mV for LBG and CTG and -15 mV for CMC, respectively. In addition, the percentage of talc depression achieved in the microflotation studies decreased in the order LBG > CTG > CMC; their respective values were 72% > 56% > 51%. Therefore, the zeta potential values agree with the adsorption and microflotation studies results observed in this study, i.e., LBG and CTG depressed talc more effectively than CMC. Lastly, bench flotation results revealed that LBG yielded the highest talc depression at 100 g/t, while CTG yielded the highest talc depression at 25 g/t. Thus, these results agreed with thermodynamic theory, viz., a low molecular weight polymer is effective at low dosages where the surface is unsaturated. In contrast, a high molecular weight polymer is effective at high dosages as there is enough quantity to cover the surface adequately.

Cassia tora gum

locust bean gum

zeta potential

alkaline gelatinisation

adsorption density

talc

Talc is a magnesium silicate, Mg₃(Si₂O₅)₂(OH)₂, a significant constituent of the gangue mineral in both the complex sulphide (Beattie et al., 2006) and PGM bearing ore bodies in South Africa (Shortridge et al., 2000). Talc is one of the softest minerals formed by altering magnesium silicates such as amphiboles and olivine (Shortridge et al., 2000; Feng et al., 2018). Talc is a magnesium silicate made of hydrous layers held together by van der Waals forces that form two different surfaces during grinding, i.e., basal cleavage planes and edges of the mineral sheet. Talc basal planes are neutral and hydrophobic as their Si-O and Mg-O bonds are not broken. On the contrary, the talc edges contain broken Mg-O and Si-O bonds; therefore, they are charged and hydrophilic (Wang & Somasundaran, 2005; Khraisheh et al., 2005). Fig. 1 illustrates the structure of talc.

Talc is a naturally floatable mineral (NFG). Hence, it is practically difficult to selectively reject talc in froth flotation without using a depressant. High talc concentrate yields the operational difficulty of the furnace at the smelter by increasing the slag viscosity and melting point. Consequentially, when the smelter continuously treats talcous concentrates, its furnace crucible life is ominously reduced due to regularly running at high temperatures (Beattie et al., 2006). Also, there are high refractory losses when furnace temperatures are too high (Feng et al., 2018). Therefore, depressants are invariably used to prevent talc flotation. As a result, talc depression using different depressants is one of the most extensively studied subjects in the field of mineral processing, e.g., guar (Jenkins & Ralston, 1998), CMC (Khraisheh et al., 2005; Wang & Somasundaran, 2005; Beaussart et al., 2010; McFadzean et al., 2011), CMC and dextrin (Miercznska-Vasilev & Beattie, 2013), guar and CMC (Cawood et al., 2005; Bicak et al., 2007).

Carboxymethyl cellulose (CMC) is the depressant commonly used to depress talc in the South African Bushveld minerals complex. However, CMC possesses a high negative charge density, leading to increased electrostatic repulsion when interacting with negatively charged minerals. Furthermore, its effectiveness is greatly influenced by the ionic strength of the pulp. As a result, higher dosages of CMC are required to achieve efficient depression, which can have adverse effects such as destabilising the froth (Wiese et al., 2008). Thus, recently, there has been a research effort on galactomannans as an alternative polymer depressant, e.g., locust bean gum (Feng et al., 2018); fenugreek seed gum (Cousins & Sudom, 2021); cassia tora (CTG) and locust bean gums (LBG) (Ngobeni & Mulaba-Bafubiandi, 2023). Characterised by their low charge density, galactomannans offer effective depression at lower dosages and remain unaffected by changes in pulp ionic strength.

Batch adsorption experiments were performed to establish the adsorption density of the interaction between the CTG, LBG, and talc. The adsorption density of these depressants onto mineral surfaces can significantly impact their performance. The results of the experiments provide insights into the adsorption mechanisms and suggest optimal conditions for their application in flotation processes. Thus, understanding the adsorption behaviour of these depressants is crucial for optimising their dosage and application in flotation processes.

Zeta potential experiments were performed using a suspension of talc particles and depressant solutions at different pH. The zeta potential measurements provide valuable insights into the surface charge characteristics and adsorption mechanisms underlying the depression process. The results highlight the influence of depressant and mineral surface properties on the electrochemical behaviour, shedding light on the suitability of these depressants for enhanced selective depression of talc.

Microflotation studies were utilised to establish the underlying talc-depressants interactions, hydrodynamic conditions, particle flotability, and pulp environment without the effect of the froth phase. Microflotation is considered a more accurate indicator of the interaction in the three flotation process phases, as it involves both the thermodynamic and kinetic characteristics of the flotation system (Bradshaw, 1997).

Finally, bench flotation studies were conducted to investigate the effectiveness of these depressants in talc depression, with the effect of froth phase and liberation accounted for. There is no published literature on alkaline gelatinised CTG and LBG as talc depressants. Consequently, no published adsorption mechanism or thermochemical data on their fundamental interaction on the talc surface exists. Therefore, this paper used adsorption, zeta potential, microflotation and bench flotation to study the adsorption mechanisms, electrochemical and talc depression with the alkaline gelatinised CTG and LBG compared to CMC.

2.1 Materials

The ore and pure talc mineral were sourced from (the Bushveld Igneous Complex, South Africa). Cassia tora gum splits from Rama Industries Ltd (Mumbai, India), locust bean gum purchased from Sigma Aldrich (Johannesburg, South Africa), and Norilose 6064 supplied by AECI Mining Chemicals (Sasolburg, South Africa) were the polymers used in the study. Hydrochloric Acid (25%, MINEMA Chemicals, South Africa), Sulphuric acid (32%, MINEMA Chemicals, South Africa), Sodium hydroxide (48%, NCP Chlorchem, South Africa), and Carbolic acid (MINEMA Chemicals, South Africa) were the chemical used for Phenol-Sulphuric acid colourimetric adsorption method.

2.2 Batch adsorption procedure

The adsorption tests were carried out on a talc sample with particle size 38 < 75 µm. Water was used to prepare a 0.01 M depressant solution. An accurately weighed 2 g of the talc was added to 250 ml beakers containing 100 ml of a depressant solution (0.01 M), each adjusted to pH between 9 and 9.5 using either 0.1 M NaOH or HCl solutions. The solutions were stirred for 30 min and centrifuged at 1000 rpm for 10 min using an EC6-100 cp centrifuge. 2 ml of the clear supernatant was mixed with 1 ml of 5% aqueous phenol solution in a test tube. Subsequently, 5 ml of concentrated sulphuric acid was added to the mixture. The samples were thereafter vortexed for 2 min. After allowing the test tubes to stand for 10 min, they were then placed in a water bath set at ambient temperature for another 30 min for further colour development. The light absorption at 490 nm was recorded on an Eppendorf U-V Bio spectrometer (Eppendorf AG, Germany). The light absorption was conducted in triplicate, and the average value was used in the final calculations. The adsorbate concentration at the equilibrium state in the solid phase was computed using Eq. (1)

The surface area of talc particle size (38 < 75µm) was measured by the Brunauer, Emmett, and Teller (BET) method, and the results are presented in Table 1.

Table 1. BET surface area and chemical formula of talc particle size 38<75µm.

	Chemical formula	BET area (m²/g)
Talc	Mg₃(Si₂O₅)₂(OH)₂	1.3540

2.3 Zeta potential procedure

All zeta potential measurements were conducted in a 0.001 M KNO₃ electrolyte solution with a Zeta Sizer Nano Series (Malvern, United Kingdom). A depressant sample of 0.04 g each was weighed and transferred into a 500 ml volumetric flask. Then, 0.001 M KNO₃ was added into the volumetric flask to make the depressant stock solution. The solution was left overnight to condition. After that, all the insolubles in the depressant solution were filtered out using 0.4 µm Millipore in-line filters. Then, 0.15 g of talc with particle size P₁₀₀ -25 µm was weighed into a 300 ml beaker. Afterwards, 120 ml filtred depressant solution was added into the beaker with the talc sample. Then, the mixture was stirred for 30 min, followed by 5 min sonication to ensure good dispersion. After sonication, the mixture was split into 60 ml aliquots. Then, the pH was adjusted and maintained at 9 using NaOH (0.1 M) or HCl (0.1 M). Thereafter, the mixture was stirred for 20 min using a magnetic stirrer. Then, 1 ml aliquot was drawn and transferred into a folded capillary while ensuring there were no bubbles in the cell. Then, the cell was placed in the Zeta Sizer Nano Series to compute the electrophoretic mobility at 25˚C. The electrophoretic mobility measurements were duplicated for quality assurance, and the results were subsequently averaged.

2.4 Microflotation procedure

2 g pure talc was weighed. Then, transferred into a beaker, and 100 ml water was added. The solution was cleaned ultrasonically for 5 min and wet screened to remove any fines present. After which, depressant 100 g/t was added and conditioned by mixing with a magnetic stirrer for 5 min. Then, the solution was transferred into the microflotation cell. The pump was started and maintained at 126 rpm. The cell was then filled with water until the water reached the overflow lip. Then, the cone was fixed in place before introducing the air at 12 ml/sec or digital flowmeter reading of 4.25 sccm. The concentrate was collected for 25 min. After that, the air was stopped. Then, the concentrate and tailing samples were collected, filtered, and dried. Afterwards, the dry masses were recorded, and the recovery and percentage depression were calculated.

2.5 Bench flotation procedure

1000 ml of synthetic water and 2 kg of ore sample were added to the rod mill. The sample was milled for 78 min to give a grind of P₈₀ -75 µm. The slurry was discharged into the flotation cell, and water was used to wash the mill and the rods. The flotation cell was filled with water to the 4.5 L mark. The pulp was agitated at 900 rpm without introducing air. Collectors were added to the cell and conditioned for 2 min. The depressant and frother were added simultaneously to the cell and conditioned for 2 min. The air valve was opened, and the airflow was maintained at 5 L/min via a rotameter. Flotation was carried out for 25 min with froth scrapping every 15 s. The pulp level was kept constant by adding water when needed. Three concentrates were collected at 0–3 min, 3–10 min, and 10–25 min intervals. After 25 min of flotation, the air was switched off. The wet concentrates masses were recorded. All the concentrates and the tailings were filtered. The samples were dried in the oven overnight at 60˚C to avoid driving off sulphur and roasting the sulphide minerals. The dry masses were recorded, and sample preparation was completed. The samples were sent to SGS (Randfontein, South Africa) for chemical analysis. Duplicate tests were conducted for this study; the results presented are the average of two independent readings. The test was repeated if the dry weights were out by 5%.

3.1 Adsorption densities.

The adsorption studies conducted in this paper yielded significant insights into the interaction between depressants and the talc surface. Fig. 2 visually presents CMC, CTG, and LBG adsorption densities on the talc surface, plotted against equilibrium concentration. The results showed that the alkaline gelatinised CTG and LBG depressants exhibited higher adsorption densities than CMC across all tested dosages. Interestingly, a key observation was that CMC displayed negligible adsorption on the talc surface until its concentration reached approximately 35 mg/l. This phenomenon can be attributed to the characteristic adsorption behaviour of polymeric depressants. Typically, these depressants initially adsorb onto the basal cleavage planes of talc and then progressively extend to cover the mineral surface until a monolayer is formed. Subsequently, the adsorption process continues onto the edges of the mineral sheet. This stepwise adsorption process increases coverage on the basal plane, which is influenced by the polymer solution concentration. This mechanism aligns with findings from previous studies. Wang and Somasundaran (2005) elucidated the initial adsorption on basal cleavage planes and subsequent edge adsorption for polymeric depressants. The research by Beaussart et al. (2010) further supported this concept by highlighting that the concentration of the polymer solution influences the extent of coverage on the basal plane.

Bicak et al. (2007) compared guar gum and CMC as talc depressants. Their study found that guar gum was effective at lower dosages than CMC. This difference in effectiveness led to the hypothesis that other galactomannans, such as CTG and LBG, might exhibit higher adsorption densities than CMC when used as depressants. However, native CTG and LBG are insoluble in cold water. Thus, they had to be alkaline gelatinised first. CTG and LBG were chosen because they share structural similarities with guar gum and their gelling properties. The experimental results supported this hypothesis, as CTG (5.8 mg/m²) and LBG (4.6 mg/m²) yielded higher adsorption densities on the talc surface than CMC (3.5 mg/m²) (Fig. 2).

One factor affecting polymer adsorption is its molecular weight. This phenomenon was investigated by Beaussart et al. (2010), who found that higher molecular weight depressants resulted in decreased adsorption onto talc surfaces. Contrary to their findings, the present study revealed a different trend when using galactomannans. This discrepancy was attributed to the distinct chemistry between CMC and galactomannans, indicating that the behaviour observed with CMC might not directly apply to galactomannans.

The chemistry of the polymer also plays a significant role in its adsorption behaviour, as highlighted by both Beaussart et al. (2010) and Khraisheh et al. (2005). However, Khraisheh et al.(2005) study focused on CMC's molecular weight; therefore, given the different chemistry of galactomannans, their findings might not fully apply. This emphasises the importance of considering the specific characteristics of each polymer. The results of the present study demonstrated that the effect of polymer chemistry was more pronounced than the effect of polymer molecular weight. This conclusion was supported by the notable differences in adsorption density between CTG and CMC, even though their molecular weights were comparable at around 300 and 200 kDa, respectively. For CMC, higher ionic strength would be needed for talc to overcome both the inter and intramolecular electrostatic repulsion between the CMC chains that hinder the formation of a dense CMC layer, ultimately affecting its adsorption capacity (Beaussart et al., 2010).

3.2 Zeta Potential

Flotation reagent adsorption plays a crucial role in altering the charge properties of mineral surfaces when they interact with solution interfaces. Zeta potential measurements are a valuable tool for assessing such alterations, allowing researchers to gain insights into changes in the electrical properties of the mineral surface due to adsorption (Zhang et al., 2021). This aspect becomes particularly relevant in flotation, where the isoelectric point (IEP) of minerals serves as a significant variable. Manipulating the surface charge of minerals through pH control enables fine-tuning their flotation behaviour (Alvarez-Silva et al., 2010). Zeta potential measurements were employed to investigate the changes in the electrical properties at the talc surface in the absence and presence of CMC, CTG and LBG. The results are demonstrated in Fig. 3. In the absence of the depressants, the zeta potential of talc was positive at a pH of 2 and negative in pH values above 2.5. The IEP value for talc in this study was ~2.2 (Fig. 3), which falls in the reported range of less than 3 (Alvarez-Silva et al., 2010; Bacchin et al., 2006; Pan et al., 2020). The zeta potential for talc increased with increasing pH until the maximum (-20 mV) was reached at pH 6, after which its zeta potential decreased with increasing pH (Fig. 3). These findings highlight the complex relationship between pH and surface charge, influencing the electrostatic interactions in flotation processes.

The differences in the adsorption behaviours of ionic CMC, nonionic CTG and LBG on the talc surface could result from their distinct metal ions' electron affinities in the mineral crystals. These electron affinities yield distinct adsorption performances on the talc surface (Morris et al., 2002; Shen et al., 2021). As a phyllosilicate mineral, talc possesses variable charges on its face and edge surfaces, influencing its isoelectric point (IEP) depending on the measurement location. According to Alvarez-Silva et al. (2015), anisotropic minerals, i.e. minerals with different charges on the edge and face, are believed to form aggregates like a house of cards under different conditions as it is not always clear where the adsorption occurs (Alvarez-Silva et al., 2010). The results, however, revealed that talc surfaces were negatively charged at all pH ranges (Fig. 3). These results were comparable to those reported in the literature by other researchers, such as Morris et al. 2002; Liu et al., 2006 and Pan et al., 2020.

Talc+CMC zeta potential was significantly affected by a change in pH. The zeta potentials were more negative at a pH lower than 6 and less negative at a pH above 6. The observed less negative at a pH above 6 with CMC-talc may be attributed to two reasons: firstly, a decrease in the electrostatic repulsion between the negatively charged edges of talc and the carboxyl groups of CMC; secondly, a shift in the CMC conformation to a coiled from an extended state at higher pH values (Morris et al., 2002; Liu et al., 2006). Interestingly, this pattern was not observed for Talc+CTG and Talc+LBG, as their zeta potentials remained relatively unaffected by pH changes. However, there was a discernible shift toward less negative zeta potentials with the addition of CTG and LBG, indicative of the presence of adsorbed polymers, as reported by Pan et al. (2020). Morris et al. 2002 also found that pH significantly influenced the zeta potential of the anionic polymers (CMC and PAM-A), while the nonionic PAM-N was unaffected.

Considering the context of PGM flotation, which occurs at pH 9 (Mhlanga et al., 2012), the zeta potential results at this pH level were particularly significant in this study. At pH 9, the zeta potential for Talc+ LBG and Talc+ CTG was -5.75 mV, while Talc+CMC was -15 mV (Table 2). These zeta potential values align with the observations from the adsorption and microflotation studies, indicating that LBG and CTG were more effective depressants for talc than CMC.

Table 2. Summary of the zeta potential results obtained at pH 9, talc only, talc + CMC, talc + CTG and Talc + LBG.

	Zeta potential (mV)
Talc	-20
Talc + CMC	-15
Talc +CTG	-5.75
Talc + LBG	-5.75

3.3 Microflotation

The outcomes of talc microflotation obtained from the present study provide a significant basis for comparison and discussion concerning existing literature. The investigation revealed that in the absence of a depressant (referred to as the blank condition), the flotability of talc was measured at 89%, as indicated in (Table 3). This outcome suggests that the talc utilised in this study could be categorised as naturally floatable gangue. Cawood et al. (2005) achieved talc recovery of 64% in the absence of a depressant after 12 min microflotation. Although, their microflotation time was shorter than 25 min in the present study. They could have achieved higher recoveries if they floated for longer times based on the shape of the curve they achieved (Cawood et al., 2005). This comparison underscores the importance of considering flotation time when assessing the effectiveness of depressants.

Table 3. Summary of microflotation results obtained with CMC, CTG, and LBG

	Recovery (%)	Depression (%)	STDEV	STD ERROR (%)

Blank	89 43 39 25	- 51 56 72	1,40 3,16 0,63 1,61	0,99 2,23 0,44 1,14
CMC
CTG
LBG

The concept of naturally floatable gangue minerals is important in mineral processing and flotation. These gangue minerals possess inherent characteristics that make them prone to attachment to air bubbles and subsequent flotation. The flotability observed in the blank condition underscores the need to employ effective depressants to selectively inhibit talc flotation. Identifying talc as naturally floatable gangue aligns with the broader understanding of mineral flotation. It emphasises the need for appropriate control strategies and reagents to ensure successful mineral separation in flotation circuits. Characterising talc flotability in the absence of depressants is a critical step toward designing effective flotation strategies for mineral processing operations.

The results further showed that all three depressants could depress talc, as illustrated by reduced talc flotability with their addition. The percentage of talc depression achieved decreased in the order LBG > CTG > CMC, and their values were 72%, 56%, and 51%, respectively (Fig. 4). CTG and LBG are complex polysaccharides. Their chemical structures are strictly hydroxyl groups. Therefore, to facilitate talc depression, the hydroxyl groups on CTG and LBG adsorbed onto the talc surface through the hydrophobic backbone. However, structurally, CMC adsorption may occur through carboxymethyl and hydroxyl groups. Thus, it may result in different adsorption and talc depression (Bicak et al., 2007). This phenomenon has been documented in previous research, with studies by Morris et al. (2002) and Shen et al. (2021) highlighting the influence of metal ions' electron affinities on adsorption behaviours.

3.4 Bench flotation

The section compares the performance of CMC, CTG, and LBG depressants on Platreef ore in terms of their ability to prevent talc from floating. To this end, talc recovery to tailings (Table 4) and talc recovery versus concentrate mass pulls were evaluated (Fig. 5 to Fig. 7). CMC can adsorb via carboxymethyl and hydroxyl groups in their structure (Bicak et al., 2007). Therefore, the presence of both neutral, hydrophobic, and charged, hydrophilic surfaces on talc, combined with the condition of the surface charge and surface metal hydroxylation, may result in different adsorption and different talc depression performance with CMC in mineral flotation (Fig. 3). The prominent accepted hypothesis is that CMC selectively adsorbs onto the talc planes firstly through hydrophobic bonding forces (Shortridge et al., 2000) and then moves onto the edges (Khraisheh., 2005).

Table 4. Summary of bench flotation results

	Mass Pull (%)	Talc Recovery %	Talc Grade (%)	Talc Depression (%)
CMC 25 g/t	13	16	10	84
CMC 50 g/t	14	15	10	85
CMC 100 g/t	13	15	11	85
CTG 25 g/t	14	17	11	83
CTG 50 g/t	14	18	12	82
CTG 100 g/t	14	16	11	84
LBG 25 g/t	15	18	11	82
LBG 50 g/t	14	14	11	86
LBG 100 g/t	14	13	10	87

The main difference between CMC, CTG, and LBG is that CMC can adsorb via carboxymethyl and hydroxyl groups in their structure (Bicak et al., 2007). On the contrary, both CTG and LBG adsorb through the hydroxyl group. Therefore, these differences in adsorbing groups govern how effectively each class of polymer interacts with a different gangue mineral. This follows that CMC is attached to the talc surface via a plane two-dimensional confirmation, whereas the CTG and LBG adsorption is through three-dimensional conformation. Therefore, the observed slightly higher talc depression of talc with LBG, especially at 100 g/t, is due to the improved adsorption of LBG onto the talc surface (Table 4). Thus, the adsorbed layer of LBG strongly shielded the talc surface from air bubbles.

Fig. 5 depicts recovery versus concentrate mass pull for CMC, CTG, and LBG at 25 g/t. The data showed that talc recovery was similar for both CMC and CTG at ~16% and was slightly lower than ~18% yielded by LBG (Fig. 5).

Fig. 6 depicts talc recovery versus concentrate mass pull for CMC, CTG, and LBG at 50 g/t. The data revealed that talc recovery decreased in the order CTG > CMC > LBG; their values were ~18%, ~15%, and ~14%, respectively.

Fig. 7 depicts talc recovery versus concentrate mass pull for CMC, CTG, and LBG at 100 g/t. The data revealed that talc recovery decreased in the order CTG > CMC > LBG; their values were ~16%, ~15%, and ~13%, respectively.

Thermodynamically, high molecular weight polymers selectively attach on the surface of the mineral because they lose little translational entropy in the solution while gaining almost the same cumulative adsorption energy. Therefore, a low molecular weight polymer will be effective at low dosages, where the surface is unsaturated. However, a high molecular weight polymer will be more effective at high dosages as there is enough to cover the surface (Fleer et al., 1993). CTG has a lower molecular weight than LBG. Thus, effective mineral surface covering can be accomplished with less LBG than CTG at higher dosages. The results in this study agreed with thermodynamic theory because at 25 g/t CTG (~16%) recovered slightly less talc than LBG (~18%) (Fig. 5), and at higher dosages (100 g/t), LGB (~13%) yield a marginally lower talc recovery than CTG (~16%) (Fig. 7). Furthermore, comparable talc recovery between CTG and LBG was attained at intermediate dosage (50 g/t) (Fig. 6). Generally, increasing the molecular weight of galactomannans depressant increased adsorption onto the talc surface. With a higher molecular weight of LBG, there would be higher hydrophobicity and, consequently, greater hydrophobic bonding forces between the LBG and the talc surfaces than with CTG (Fig. 3).

Higher molecular weight polymers have strong hydrophobicity. Consequently, stronger hydrophobic bonding forces would be between the talc surface and the high molecular weight polymer (Rath et al., 1997). The slightly higher talc depression with LBG than CTG (Table 4) is hypothesised to be due to a thicker adsorbed layer and higher adsorption density (Fig. 3) resulting from the extension of the tails with increasing concentration (Shortridge et al., 2000).

The linear relationship between talc recovery and concentrate mass pull shows that all three depressants at all three dosages tested were selective against talc (Fig. 5; Fig. 6; Fig. 7). Consequently, talc was presumably recovered predominately through mechanical processes, i.e., physical entrapment and hydraulic entrainment, rather than flotation.

3.5 Bench flotation statistical analysis

Analysis of Variance (ANOVA) was utilised to evaluate the statistical significance of the effects of changing parameters relative to the inherent experimental error. To this end, Microsoft Excel data analysis add-in was used to compute the mean square (MS), variance, P-values and degrees of freedom (df). Thus, the significance of the effect of each parameter on bench flotation performance was determined by looking at the P-values. In the minerals beneficiation, effects with P ≥ 0.10 are generally considered 'not significant', indicating the observations are likely due to random chance rather than a meaningful relationship. Conversely, effects with P ≤ 0.05 are considered 'significant', suggesting a strong possibility that the results are due to the effects investigated (Bradshaw, 1997). In this study, effects with P ≤ 0.01 were regarded as highly significant and denoted by (***), P of 0.05 ≥ 0.01 signifies significant and denoted by (**), P of 0.1 ≥ 0.05 (*) implied a slightly significant and (~) denotes not significant effects (P ≥ 0.10). The results showed that the talc recovery differences observed in this study were highly significant, as illustrated by a P-value of 0.007 (Table 5).

Table 5. Summary of a single factor ANOVA of talc recovery

Groups	Count	Sum	Average	Variance
CMC 25 g/t	2	31.27	15.64	1.2641
CMC 50 g/t	2	29.94	14.97	0.0032
CMC 100 g/t	2	29.35	14.68	0.0113
CTG 25 g/t	2	33.86	16.93	1.2168
CTG 50 g/t	2	36.96	18.48	1.1250
CTG 100 g/t	2	31.86	15.93	5.4450
LBG 25 g/t	2	35.44	17,72	0.2592
LBG 50 g/t	2	27.59	13.80	0.1201
LBG 100 g/t	2	26.26	13.13	0.0200

ANOVA
Source of Variation	SS	df	MS	F	P-value	F crit
Between Groups	50.39228	8	6.299035	5.989858	0.007347~	3.229583
Within Groups	9.46455	9	1.051617

The adsorption mechanism, adsorption thermodynamics, and depression of talc using CTG, LBG, and CMC were investigated through adsorption studies and microflotation experiments. The following main conclusions were drawn. Talc flotability in the absence of the depressant was 89% this implied that the talc used in this study was naturally floatable. The adsorption studies revealed that CTG yielded the highest talc adsorption density, followed by LBG and CMC, and their adsorption densities were 5.8 mg/m², 4.6 mg/m² and 3.5 mg/m², respectively. PGM flotation occurs at pH 9. Therefore, the zeta potential results at this pH were given more focus in the present study. The zeta potential values at pH 9 were -5.75 mV for LBG and CTG and -15 mV for CMC, respectively. In addition, the percentage of talc depression achieved in the microflotation studies decreased in the order LBG > CTG > CMC; their respective values were 72%, 56% and 51%. Therefore, the zeta potential values agree with the adsorption and microflotation studies results observed in this study, i.e., LBG and CTG depressed talc more effectively than CMC. Lastly, bench flotation results revealed that LBG yielded the highest talc depression at 100 g/t, while CTG yielded the highest talc depression at 25 g/t. Thus, these results agreed with thermodynamic theory, viz., a low molecular weight polymer is effective at low dosages where the surface is unsaturated. In contrast, a high molecular weight polymer is effective at high dosages as there is enough quantity to cover the surface adequately. The linear relationship between talc recovery and concentrate mass pull shows that all three depressants at all three dosages tested were selective against talc. Consequently, talc was presumably recovered predominately through physical entrapment and hydraulic entrainment rather than flotation.

CRediT authorship contribution statement

Walter Amos Ngobeni developed the project, planned the experiments, carried out the experiments and sample preparation, interpreted the results, and wrote the manuscript. Antoine F. Mulaba-Bafubiandi supervised the work.

Ethics approval and consent to participate

Not applicable

Consent for publication

Not applicable.

Competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Financial interest

No funds, grants, or other support were received. The authors have no financial or proprietary interests in any material discussed in this article.

Data Availability

The datasets used or analysed during the current study are available from the corresponding author upon reasonable request.

Acknowledgements

We are grateful for the role that AECI Mining Chemicals staff played in the success of this work. They provided reagents and allowed us to use their facilities to conduct the experiments. Ms Boitumelo Baruti and Mr Rendani Luvhengo from AECI Mining Chemicals R&D for their practical help with adsorption and zeta potential studies, respectively.

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No competing interests reported.

Alkaline gelatinised cassia tora and locust bean gums as talc depressants: Adsorption and thermochemical aspect

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Abstract

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1. Introduction

2. Materials And Method

3. Results And Discussion

4. Conclusion

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Additional Declarations

Status:

Journal Publication

Version 1