Separation of Lead from Chalcopyrite Slurry Using Resin-in-Pulp

Abstract

In this study, Resin-in-Pulp (RIP) technology is used to separate Pb from a chalcopyrite slurry. Solvent-impregnated resin, Lewatit® VP OC 1026, which contains di(2-ethylhexyl) phosphoric acid (D₂EHPA) in a macroporous polystyrene matrix was used, as the functional group exhibits selectivity for Pb over Cu. Adsorption pH, kinetics, as well as resin and CuSO₄ concentrations were investigated. The results show that the kinetics of Pb and Cu loading are fast, reaching the adsorption equilibrium within 30 min. The equilibrium pH of 2 was chosen as optimum for operation in order to achieve a high Pb extraction rate and extent as well as selectivity for Pb over Cu. High Cu(II) concentration in solution results in Pb(II) requiring a larger amount of resin for the same degree of extraction . Regeneration and reuse tests show that the loss of adsorption capacity happens in the 1st and 2nd cycles and then the adsorption capacity stabilises for the 3rd cycle.

Introduction

Resin-in-Pulp (RIP) technology has been widely used to purify and enrich metal ions from hydrometallurgical leach slurries, including gold , uranium and nickel . In the RIP process, the ion exchange resin beads contact the leach slurry and metals are selectively loaded from solution onto the resin. The loaded resin is subsequently separated from the leach slurries by screens and loaded metal ions on the resin are eluted in a static bed ion exchange column . The main advantages of this technology include promoting leaching efficiency and eliminating stages of primary counter-current decantation or filter cake washing.

The selection of ion exchange resin is an important consideration in terms of overall process efficiency . Firstly, the functional group type must be identified. For anion exchange resins, strong-base anion exchange resins exhibit higher adsorption affinity for gold cyanide species than other base metal (Ni, Co, Fe) cyanide species in cyanide leach slurries [1]. Similarly, in uranium alkaline leach pulps, the affinity order of strong-base anion exchange resin [2] is [UO₂(CO₃)₃]⁴⁻ > MoO₄²⁻ > [UO₂(CO₃)₂]²⁻ > SO₄²⁻ > CO₃²⁻ > NO₃⁻ > Cl⁻ > HCO₃⁻, indicating that strong-base resin can selectively extract uranium species from alkaline leach solution . For cation exchangers, a chelating-type ion exchange resin with an iminodiacetic acid functional group (Lanxess^® TP 207 XL) has been used to extract nickel from nickel laterite leach slurries [3]. However, the number of industrial applications of RIP remains small due to low selectivity compared with solvent extraction , slow kinetics and the high cost of conventional ion exchange resins. The cost of resin is a critical consideration as there tend to be higher resin losses in an in-pulp circuit due to additional resin handling causing physical degradation.

The higher selectivity of solvent extractants for certain applications can be approached in the resin configuration using solvent-impregnated resins (SIRs) that are comprised of a polymeric matrix impregnated with the solvent extraction reagent. Instead of firmly forming chemical bonds, extractant molecules with hydrophobic alkane chains physically adsorb on the hydrophobic crosslinked polystyrene matrix, leading to this solvent-impregnated structure. Solvent impregnated resin is relatively easy to prepare which means the cost is not high and the products combine the unique features and process advantages of both solvent extraction and ion exchange resin . Di(2-ethylhexyl)phosphoric acid (D₂EHPA) is a well-known solvent extractant, which exhibits the following selectivity order as a function of increasing pH [4]: Fe³⁺ > Zn²⁺ > Pb²⁺ > Cd²⁺ > Ca²⁺ > Mn²⁺ > Cu²⁺ > Co²⁺ > Ni²⁺ >>> Alkali. The selectivity order indicates that D₂EHPA can preferentially adsorb Pb²⁺ ion from solution containing Cu²⁺ ion. In this work, the potential application of D₂EHPA-impregnated resin (Lewatit® VP OC 1026 manufactured by Lanxess) to separate Pb from a chalcopyrite slurry was studied.

Experimental

Materials and Reagents

A natural chalcopyrite mineral specimen with no measureable lead was ground to 100% passing a 38 µm (400 mesh). Analytical grade concentrated sulphuric acid, nitric acid, Pb(NO₃)₂, PbSO₄, Cu(NO₃)₂ and CuSO₄ were used in the experiments. The stock solutions of Pb(II) and Cu(II) (2.5 mmol/L for each ion) were prepared by dissolving appropriate amounts of metal salts in deionized water.

Methods

Batch adsorption experiments were used to determine the adsorption kinetics and selectivity based on pH, and RIP performance for this application. The kinetics and selectivity experiments were carried out by shaking a measured amount of resin with 100 mL of working solution with a certain metal ion concentration. The pH of the working solutions was adjusted by adding diluted nitric acid, sulfuric acid , or sodium hydroxide solutions as required. RIP tests were conducted by shaking set amounts of PbSO₄ powder and 10 g chalcopyrite powder with 100 mL of 3 g/L CuSO₄ solution at pH = 2. The samples were shaken for a predetermined time at 298 K and the solids were separated by filtration . Initial and equilibrium Pb(II) and Cu(II) ion concentrations in the aqueous solutions were determined by using flame atomic absorption spectrometry (AAS).

The extraction percentage (% E) was calculated using Eq. 1:

$E\% = \frac{{m_{1} }}{{m_{2} }} \times 100\%$

(1)

where m₁ is mass of metal ion adsorbed by resin, m₂ is total mass of metal ion in initial solution.

The distribution ratio of the metal, D, was calculated as the ratio of mass of metal ion in resin to that in the aqueous phase at equilibrium, calculated using Eq. 2.

$D = \frac{{m_{1} }}{{m_{2} - m_{1} }}$

(2)

From the D values, the separation factor (β) of Pb over Cu was calculated using Eq. 3:

$\beta_{Pb/Cu} = \frac{{D_{Pb} }}{{D_{Cu} }}$

(3)

Elution of metals from loaded resin was achieved by contacting the resin with 6 M hydrochloric acid , followed by diluted H₂SO₄ solution (pH = 2). After elution, the regenerated resin was used for Pb (II) adsorption from a saturated PbSO₄ solution.

Results and Discussion

To determine an optimum contact time between the OC 1026 resin, the adsorption of metal ions from single metal solutions was measured as a function of contact time. The result of the loading kinetics experiments are presented in Fig. 1. The results show that Pb and Cu extractions using D₂EHPA-impregnated resin were fast with most of the reaction being completed within the first 10 min, equilibrium loadings of >90% appear to be achieved by 30 min at these conditions. Compared to conventional ion exchange resins with chemically bonded functional groups, D₂EHPA molecules physically adsorbed on solvent impregnated resin can react with metal ions in solution faster, forming a stable metal-D₂EHPA complex in the resin matrix.

../images/468727_1_En_174_Chapter/468727_1_En_174_Fig1_HTML.gif — Fig. 1
Adsorption kinetics for Cu(II) , Pb(II) loading onto VP OC 1026 resin. (pH = 2.4, T = 298 K. Pb test: 2.5 mmol/L Pb(NO₃)₂, 25 mL solution/g resin; Cu test: 2.5 mmol/L Cu(NO₃)₂, 15 mL solution/g resin)

The effect of equilibrium pH on metal extraction percentage is illustrated in Fig. 2. Compared with Cu(II), OC 1026 resin preferentially adsorbs Pb(II) in the pH range of 0.5–3.0, indicating that in a mixed ion solution, it can be feasible to separate Pb(II) ion from Cu(II) at lower pH. To achieve high degrees of Pb extraction and significant Pb/Cu selectivity , a pH of 2 was selected as the optimum, where Pb extraction in a single contact is about 74% and the copper separation factor (β_Pb/Cu) is about 10.

../images/468727_1_En_174_Chapter/468727_1_En_174_Fig2_HTML.gif — Fig. 2
Effect of pH on adsorption behaviour of Cu(II) , Pb(II) onto VP OC 1026 resin. (T = 298 K. Pb test: 2.5 mmol/L Pb(NO₃)₂, 16.7 mL solution/g resin; Cu test: 2.5 mmol/L Cu(NO₃)₂, 16.7 mL solution/g resin)

The adsorption of Pb(II) and Cu(II) onto VP OC 1026 resin in chalcopyrite slurry (10% chalcopyrite ) saturated PbSO₄, was studied at different concentrations of CuSO₄. The results in Fig. 3a show that the Pb(II) concentration was effectively decreased from 4.2 to 0.1 mg/L with resin concentrations of 5 g resin/100 mL solution where the initial lead was saturated with respect to PbSO₄. After introducing CuSO₄ and 10% solids content, the Pb concentration decreased slowly to 1.12 and 1.98 mg/L at 0.75 and 3.03 g/L CuSO₄, respectively, using 7.5 g resin/100 mL solution. The lower Pb removal efficiency is attributed to the competitive adsorption of Cu(II) onto the resin due to its high concentration compared to Pb(II). The Cu extraction percentages shown in Fig. 3b increased to 3.87 and 5.90% for 0.75 and 3.03 g/L initial CuSO₄ concentrations respectively, when 7.5 g resin was added into the slurries. The results indicate that high Cu(II) concentration reduces the percentage of Pb(II) removed and a larger dosage of resin is needed.

../images/468727_1_En_174_Chapter/468727_1_En_174_Fig3_HTML.gif — Fig. 3
Effect of resin amount on adsorption of Pb(II) and Cu(II) onto VP OC 1026 resin under resin-in-pulp conditions. (T = 298 K, pH = 2, 100 mL solution for each test, Solution 1: saturated PbSO₄ solution, Solution 2: saturated PbSO₄ + 0.75 g/L CuSO₄ + 10% chalcopyrite (solid content), Solution 3: saturated PbSO₄ + 3.03 g/L CuSO₄ + 10% chalcopyrite (solid content))

Elution of Cu(II) and Pb(II) from loaded resin was achieved using 6 M hydrochloric acid (20 mL solution/g resin) for 0.5 h at 298 K, followed by diluted H₂SO₄ solution at pH = 2. After elution, the regenerated resin was used to adsorb Pb(II) in the next cycle. To illustrate the reusability of VP OC 1026 resin, Fig. 4 shows three adsorption -elution cycles indicating the loss of adsorption capacity happens in the 1st and 2nd cycles and the adsorption capacity becomes stable in the 3rd cycle. This decreased capacity is attributed to the loss (leakage) of physically bonded D₂EHPA from the resin matrix (crosslinked polystyrene) during the elution process.

../images/468727_1_En_174_Chapter/468727_1_En_174_Fig4_HTML.gif — Fig. 4
Adsorption of Pb(II) onto regenerated VP OC 1026 resin in saturated PbSO₄ solution. (T = 298 K, pH = 2, 100 mL solution; after each adsorption test, loaded resin was eluted with 6 M HCl and washed with pH = 2 H₂SO₄ solution for the next cycle)

Conclusion

Solvent-impregnated resin, VP OC 1026, was evaluated for use in separating Pb from chalcopyrite slurry. The results show that the kinetics of Pb and Cu extractions are very fast and reach equilibrium adsorption levels within 30 min. The equilibrium pH = 2 was chosen as the optimum pH for operation to achieve high Pb extraction rate and good Pb/Cu selectivity . In a single contact under these conditions, a Pb extraction of 74% was attained and the separation factor (β_Pb/Cu) was about 10. Resin-in-pulp tests indicated that a higher background Cu(II) concentration in the solution reduces the percentage of Pb(II) adsorbed and necessitates the use of a higher resin dose to achieve comparable results to those obtained in copper -free solutions. Regeneration and reuse cycle tests showed that resin capacity stabilized after two cycles with a negligible decline in the third cycle.

Acknowledgements

This research was conducted by the Australian Research Council Australian Copper-Uranium Transformation Research Hub (project number IH130200033) and funded by the Australian Government.