Adsorption Properties of a Polyamine Special Ion Exchange Resin for Removing Molybdenum from Ammonium Tungstate Solutions

Abstract

A polyamine special ion exchange resin was used to adsorb Mo from ammonium tungstate solutions. The effects of adsorption time, S²⁻ concentration, adsorption temperature, CO₃²⁻ concentration, mass ratio of WO₃ to Mo, and Mo concentration on the Mo and WO₃ adsorption capacities were investigated. Energy dispersive spectrometer plane scans were used to study the distributions of Mo, W, S, and Na on the loaded polyamine special ion exchange resin and the desorbed polyamine special ion exchange resin. The results showed that the polyamine special ion exchange resin performed well during adsorption and desorption. Under the optimum conditions for the static adsorption experiments, the adsorption capacities for Mo and WO₃ were 99.29 mg/mL and 31.97 mg/mL, respectively, and the desorption rates for Mo and WO₃ were 99.35% and 99.43%, respectively. Adsorption and desorption of molybdenum and tungsten on the polyamine special ion exchange resin were investigated by dynamic adsorption experiments with an ammonium tungstate solution containing 125.0 g/L WO₃, 12.50 g/L Mo, 15.65 g/L S²⁻, and 0 g/L CO₃²⁻. The adsorption capacities for Mo and WO₃ were 53.48 mg/mL and 9.79 mg/mL, and the adsorption rates for Mo and WO₃ were 99.05% and 1.81%, respectively. The loaded polyamine special resin was desorbed with a 45 g/L sodium hydroxide solution, and the dynamic desorption rates for Mo and WO₃ were 99.02% and 99.29%, respectively.

1. Introduction

Tungsten and molybdenum are both VIB elements in the periodic table [1]. Due to the lanthanide contraction, their atomic radii are close [2], their properties are similar, and it is difficult to separate them [3,4]. To remove molybdenum from an ammonium tungstate solution efficiently [5], researchers have developed a variety of molybdenum removal processes [6,7,8,9]. The molybdenum sulfide precipitation method realizes molybdenum precipitation under acidic conditions, which readily produces toxic and harmful gases. The selective precipitation method [10,11] introduces a copper salt to form CuMoO_xS_4−x precipitates and achieve efficient molybdenum removal, and it is widely used. However, during molybdenum removal, molybdenum removal slag (a hazardous solid waste) is generated, and some tungsten is coprecipitated. The solvent extraction separation method [12,13,14] has strong adaptability [15] but easily contains organic matter [16]. The evaporative crystallization method is only applicable to coarse separations of tungsten and molybdenum and cannot realize deep separation. The resin adsorption method [17,18] is easy to apply, stable, and does not leave waste residue [19]. When treating ammonium tungstate solutions with high molybdenum contents, the molybdenum adsorption capacity is low, and the adsorption efficiency varies [20].

Resin adsorption technology for molybdenum removal uses molybdenum and sulfur to form the stable thiomolybdate under weakly alkaline conditions, which is preferentially adsorbed on the resin to affect the separation of tungsten and molybdenum. A strongly basic anion exchange resin (201 × 7) [21], which is very stable in combination with thiomolybdate, realizes the efficient separation of tungsten and molybdenum. However, due to the high affinity, it is difficult to fully desorb the loaded resin. Generally, oxidants (hydrogen peroxide or sodium hypochlorite) should be added, resulting in poor stability of the resin, low adsorption efficiency, and few use cycles. The weakly basic D290 macroporous anion exchange resin has very high molybdenum adsorption capacity and efficiency, but it is difficult to desorb and recycle the loaded resin. Huo et al. carried out a study on the adsorption of molybdenum by the weakly basic D309 ion exchange resin (primary amine type) [22]. The adsorption capacity for molybdenum reached 31 mg/mL, and the desorption rate reached 97.30%.

With the shortage of high-quality tungsten mineral raw materials, complex low-grade tungsten ore with high molybdenum content has become an important tungsten and molybdenum resource. An increase in the Mo/W ratios in mineral raw materials leads to higher Mo/W concentration ratios in the leaching solutions, which further increases the difficulty of separating tungsten and molybdenum. Therefore, it is necessary to study new and efficient molybdenum removal technologies to adapt to the changes in tungsten smelting mineral raw materials. Based on the above situation, the adsorption of molybdenum from ammonium tungstate solutions was studied with a polyamine special resin. Through static adsorption and dynamic adsorption experiments, the molybdenum adsorption performance of the polyamine special resin was determined, and the molybdenum removal parameters were optimized. The aims of the study are to provide an efficient method for removing molybdenum from ammonium tungstate solutions, to reduce the cost of separating tungsten and molybdenum, and to improve resin adsorption in the tungsten molybdenum separation process.

2. Materials and Methods

2.1. Materials

An ammonium tungstate sulfide solution was prepared by mixing in the laboratory. The polyamine special resin, a macroporous weakly basic anion exchange resin (D363) with a water content of 40%, a total volume exchange capacity of 3.40 mmol/mL, a wet true density of 1.10 g/mL, resin particle sizes of 0.315–1.25 mm, a percentage of resin particles ≥ 96%, and a ball percentage ≥ 98.0%, was prepared by a resin production company in Xi’an. The resin structure is shown in Figure 1. Anhydrous Na₂CO₃ (AR) from Shanghai Zhanyun Chemical Co., Ltd. (Shanghai, China)., was used to regulate the concentration of CO₃²⁻ in the solution. NaOH (AR), Sinopharm Chemical Reagent Co., Ltd. (Beijing, China)., was used to prepare a desorption agent. (NH₄)₆Mo₇O₂₄·4H₂O (AR), Xilong Science Co., Ltd. (Beijing, China)., was used to regulate the Mo solubility in the solution. The concentrations of WO₃ and Mo in the solution were determined with thiocyanate spectrophotometry. The S⁻ concentration in the solution was determined by titration. The elemental distributions and morphologies of the loaded resin and desorbed resin were characterized with a Gemini Sigma 300/VP SEM system.

2.2. Test Method

2.2.1. Resin Pretreatment

The polyamine special resin was first soaked in pure water for 48 h (pure water does not pass through the resin layer), soaked in 5% NaOH solution for 24 h (NaOH solution does not pass through the resin layer), and then washed with pure water. After washing to a pH value of 8–9, the samples were soaked in 5% dilute hydrochloric acid solution for 8 h (the hydrochloric acid solution does not pass through the resin layer). Finally, the mixture was washed with pure water until the pH of the effluent was 5–6, and then the resin pretreatment was complete. The pretreated resin was used for subsequent tests.

2.2.2. Static Adsorption Tests

The prepared ammonium tungstate solution was placed in a glass beaker, and then the beaker was placed in a stirred water bath with a magnetic particle. Polyamino special resin was added to control the stirring speed, water bath temperature, and adsorption time. After the experiment was completed, the sample was filtered, washed, collected, and mixed well, and the concentrations of Mo and WO₃ were measured, and the capacities of the polyamino special resin for adsorption of Mo and WO₃ were calculated. After adsorption, static desorption was conducted, and the appropriate volume of the desorption agent, NaOH concentration in the desorption agent, desorption time, desorption temperature, and stirring speed were controlled. After desorption, washing was conducted, the desorption solution and washing solution were collected, samples were taken to measure the concentrations of Mo and WO₃, and the desorption rate was calculated [22].

Static adsorption capacity: Q_e = (M₁ − M₂ − M₃)/V₁

(1)

Static desorption rate: E_e = M₄/(M₁ − M₂ − M₃) × 100%

(2)

Q_e is the adsorption capacity for Mo or WO₃ (mg/mL). E_e is the desorption rate (%) for Mo or WO₃. V₁ is the volume of polyamine special resin (mL). M₁ is the mass (mg) of Mo or WO₃ in the adsorbed stock solution. M₂ is the mass of Mo or WO₃ in the solution after adsorption (mg). M₃ is the mass (mg) of Mo or WO₃ in the washing solution after adsorption. M₄ is the mass of Mo or WO₃ in the desorption solution (mg).

2.2.3. Dynamic Adsorption Test

The pretreated polyamine special resin was measured and added to a simulated exchange column, and the flow of the prepared ammonium tungstate sulfide solution was controlled with a peristaltic pump and added to the simulated exchange column for adsorption. The effluent liquid from resin adsorption was collected and mixed well, and samples were taken to measure the concentrations of molybdenum and tungsten. When the molybdenum concentration in the adsorption effluent collected from the simulated exchange column reached a set value, it was considered a result of dynamic adsorption leakage of the resin molybdenum. In case of leakage, the exchange was stopped immediately, the resin was washed with pure water, and the concentrations of molybdenum and tungsten were measured, and the capacity of the polyamine special resin to adsorb molybdenum and tungsten was calculated. After washing, the NaOH solution was used 2 more times for circulating desorption, the circulating desorption solution was collected, and the concentrations of molybdenum and tungsten were measured. After the desorption was completed, regeneration (the regenerant was composed of 5% hydrochloric acid and 1% H₂O₂ mixed solution) and washing were conducted, and then the samples were prepared for the next test [22].

Dynamic adsorption capacity: Q₁ = (M₅ − M₆ − M₇)/V₂

(3)

Dynamic desorption rate: E₁ = M₈/(M₅ − M₆ − M₇) × 100%

(4)

Q₁ is the dynamic adsorption capacity of Mo or WO₃ (mg/mL). E₁ is the Mo or WO₃ desorption rate (%). V₂ is the volume of polyamine special resin (mL). M₅ is the mass (mg) of Mo or WO₃ in the original solution adsorbed by the simulated ion exchange column. M₆ is the mass of Mo or WO₃ in the effluent after adsorption (mg). M₇ is the mass (mg) of Mo or WO₃ in the washing solution after adsorption. M₈ is the mass of Mo or WO₃ in the desorption solution (mg).

3. Results and Discussion

3.1. Static Adsorption Test

3.1.1. Effect of Adsorption Time on Molybdenum and Tungsten Adsorption Capacities for the Polyamine Special Resin

The prepared ammonium homomolybdate tungstate solution (750 mL, WO₃ 125.0 g/L, Mo 12.25 g/L, S²⁻ 14.65 g/L, CO₃²⁻ 0 g/L, pH 8.5) was put into a 2000 mL glass beaker, 30 mL of pretreated polyamine special resin was added, and static adsorption was performed in a water bath stirred with a magnetic particle. The stirring speed was 90 r/min, and the adsorption temperature was 30 °C. The relationship between the adsorption capacity of the polyamine special resin Mo and WO₃ and the change in adsorption time was investigated. The test results are shown in Figure 2.

Figure 2 shows that with the extension of adsorption time, the Mo adsorption capacity of the polyamine special resin gradually increased, while the WO₃ adsorption capacity gradually decreased. When the adsorption time reached 240 min, the Mo adsorption capacity remained almost unchanged. At this time, the Mo adsorption capacity was very high, reaching 97.51 mg/mL, and the WO₃ adsorption capacity was low, 31.90 mg/mL, indicating that this special resin is suitable for adsorbing Mo from ammonium tungstate solutions with high concentrations of Mo. During the adsorption process, MoO_xS_4−X²⁻ was preferentially adsorbed, but at the initial stages of adsorption, there were many adsorption sites on the resin. Due to the high concentration of WO₃ in the stock solution, the resin adsorbed some of the WO₃. However, in the later stages of adsorption, the WO₃ adsorbed on the resin was gradually replaced by MoO_xS_4−X²⁻. Therefore, in the later stages of adsorption, the Mo adsorption capacity gradually increased, and the WO₃ adsorption capacity gradually decreased.

3.1.2. Effect of S²⁻ Concentration on the Molybdenum and Tungsten Adsorption Capacities of the Polyamine Special Resin

A total of 750 mL of the prepared ammonium homomolybdate tungstate solution (WO₃ 125.0 g/L, Mo 12.25 g/L, CO₃²⁻ 0 g/L, pH 8.5) was placed into a 2000 mL glass beaker, 30 mL of pretreated polyamine-based special resin was added, and static adsorption was performed in a stirred water bath with a magnetic particle. The adsorption time was 240 min, the stirring speed was 90 r/min, and the adsorption temperature was 30 °C. The relationship between the Mo and WO₃ adsorption capacities of the polyamine-based special resin and the S²⁻ concentration in the adsorption solution was investigated. The test results are shown in Figure 3.

The polyamine special resin preferentially adsorbed MoO_xS_4−X²⁻, but MoO_xS_4−X²⁻ has multiple forms, and the order of preferential adsorption decreased as MoS₄²⁻ > MoOS₃²⁻ > MoO₂S₂²⁻ > MoO₃S²⁻. MoO₄²⁻ in the ammonium tungstate solution reacted with S²⁻ from the sulfurizing agent to generate MoO_xS_4−X²⁻, which was a step reaction. The generation route was MoO₃S²⁻→MoO₂S₂²⁻→MoOS₃²⁻→MoS₄²⁻. When the concentration of S²⁻ was low, MoS₄²⁻ was not fully formed, resulting in a decrease in the Mo adsorption capacity. When the concentration of S²⁻ was too high, excess S²⁻ was directly adsorbed by the polyamine special resin. Figure 3 shows that the S²⁻ concentration in the control sample was positively correlated with the Mo concentration. Generally, with a S²⁻ concentration ≥ 2.0 g/L and a Mo concentration ≤ 3.0 g/L, the Mo adsorption capacity was high, and the WO₃ adsorption capacity was low.

3.1.3. Effect of Temperature on Molybdenum and Tungsten Adsorption by the Polyamine Special Resin

The prepared ammonium homomolybdate tungstate solution (750 mL, WO₃ 125.0 g/L, Mo 12.25 g/L, S²⁻14.65 g/L, CO₃²⁻ 0 g/L, pH 8.5) was put into a 2000 mL glass beaker, then 30 mL of pretreated polyamine based special resin was added, and static adsorption was performed in a stirred water bath with a magnetic particle. The adsorption time was 240 min, and the stirring speed was 90 r/min. The relationships between the Mo and WO₃ adsorption capacities of the polyamine-based special resin and the adsorption temperature were investigated. The test results are shown in Figure 4.

The formation of thiomolybdate is an endothermic process (MoO₃S²⁻→MoO₂S₂²⁻→MoOS₃²⁻→ MoS₄²⁻) [23]. Therefore, the adsorption temperature was increased from 25 °C to 30 °C, which favored the stable generation of MoS₄²⁻. At the same time, the activity of the polyamine special resin was also improved, and the Mo adsorption capacity was increased. Some of the WO₃ initially adsorbed on the resin was replaced, resulting in a decrease in the level of WO₃ adsorption. When the adsorption temperature was higher than 30 °C, the stability of the polyamine special resin decreased with increasing adsorption temperature, which led to decreases in the Mo and WO₃ adsorption capacities. In addition, the adsorption temperature was too high, and (NH₄)₂S in the adsorption solution was easily volatilized, which is not conducive to adsorption. Therefore, the adsorption temperature was controlled at 30 °C.

3.1.4. Effect of CO₃²⁻ Concentration on the Molybdenum and Tungsten Adsorption Capacities of the Polyamine Special Resin

The prepared ammonium homomolybdate tungstate solution (750 mL, WO₃ 125.0 g/L, Mo 12.25 g/L, S²⁻ 14.65 g/L, pH 8.5) was put into a 2000 mL glass beaker, then 30 mL of pretreated polyamine special resin was added, and static adsorption was carried out in a water bath stirred with a magnetic particle. The adsorption time was 240 min, the stirring speed was 90 r/min, and the adsorption temperature was 30 °C. The relationships between the Mo and WO₃ adsorption capacities of the polyamine special resin and the CO₃²⁻ concentration in the original adsorption solution were investigated. The test results are shown in Figure 5.

Figure 5 shows that upon increasing the CO₃²⁻ concentration from 0 g/L to 120 g/L, the Mo and WO₃ adsorption capacities of the polyamine special resin gradually decreased. During adsorption by the resin, the increased CO₃²⁻ concentration led to the occupation of the vacant sites on the resin, resulting in a decrease in the adsorption capacities for Mo and WO₃. Therefore, to ensure a high Mo adsorption capacity for the resin, the lower the CO₃²⁻ concentration in the adsorption solution, the better.

3.1.5. Effect of the Tungsten to Molybdenum Mass Ratio in the Ammonium Tungstate Solution on the Molybdenum and Tungsten Adsorption Capacities of the Resin

A total of 750 mL of the prepared ammonium homomolybdate tungstate solution was placed into a 2000 mL glass beaker, 30 mL of pretreated resin was added, and static adsorption was conducted in a stirred water bath with magnetic particles. The adsorption time was 240 min, the stirring speed was 90 r/min, the adsorption temperature was 30 °C, the CO₃²⁻ concentration was 0 g/L, and the S²⁻ concentration of the control was ≥2.0 g/L and the Mo concentration was ≤3.0 g/L. The relationship between the Mo and WO₃ adsorption capacities of polyamine resin and the mass ratio of WO₃ and Mo in the adsorption solution (the WO₃/Mo mass ratios were 10/1, 15/1, 20/1, and 25/1) was studied. The test results are shown in Figure 6.

Figure 6 shows that with increases in the WO₃ to Mo mass ratio in the adsorption solution, the Mo adsorption capacity gradually decreased, and the WO₃ adsorption capacity gradually increased. Larger WO₃ to Mo mass ratios in the adsorption solution led to greater differences between the WO₃ concentration and the Mo concentration. WO₃ exhibited competitive adsorption with Mo, resulting in a decrease in the Mo adsorption capacity.

3.1.6. Effect of Molybdenum Concentration in Ammonium Tungstate Solution on Molybdenum and Tungsten Adsorption Capacity of Resin

The prepared ammonium homomolybdate tungstate solution (750 mL, WO₃ 125.0 g/L, CO₃² 0 g/L, pH 8.5) was put into a 2000 mL glass beaker, then 30 mL of pretreated polyamine-based special resin was added, and static adsorption was conducted in a water bath stirred with a magnetic particle. The adsorption time was 240 min, the stirring speed was 90 r/min, and the adsorption temperature was 30 °C. The relationship between the Mo and WO₃ adsorption capacities of the polyamine special resin and the Mo concentration in the adsorption solution was determined with various Mo and sulfide concentrations (Mo 10 g/L, S²⁻ 12.65 g/L; Mo 12.5 g/L, S²⁻ 14.65 g/L; Mo 15 g/L, S²⁻ 17.10 g/L; and Mo 17.50 g/L, S²⁻ 8.54 g/L). The test results are shown in Figure 7.

Figure 7 shows that with increasing Mo concentration in the ammonium tungstate solution, the Mo adsorption capacity of the polyamine special resin gradually increased, and the WO₃ adsorption capacity gradually decreased. When the concentration of Mo in the adsorption solution was 12.50 g/L, the adsorption capacities of Mo and WO₃ were 99.17 mg/mL and 31.26 mg/mL, respectively. When the concentration of Mo in the adsorption solution was increased to 17.50 g/L, the adsorption capacities of Mo and WO₃ were 102.73 mg/mL and 27.78 mg/mL, respectively. The polyamine special resin used in the test had a total volume exchange capacity of 3.40 mmol/mL, which was a significant advantage for high Mo adsorption capacity.

3.1.7. Static Desorption

For the static adsorption tests, 120 mL of the pretreated amino special resin was measured and placed in a 5000 mL plastic cup, and 3000 mL of sulfurized ammonium tungstate solution was added (WO₃ 125.0 g/L, Mo 12.50 g/L, CO₃²⁻ 0 g/L, S²⁻ 15.65 g/L, pH 8.5). The stirring speed was controlled at 90 r/min, the adsorption time was 240 min, and the adsorption temperature was 30 °C. After adsorption and washing, the adsorption capacities of the loaded resin for Mo and WO₃ were calculated as 99.29 mg/mL and 31.97 mg/mL, respectively.

Static desorption: 30 mL of the loaded polyamine special resin was measured for each test and placed in a 500 mL glass beaker. The volume of the desorption agent was 180 mL, the stirring speed was 90 r/min, the temperature of the desorption water bath was 30 °C, and the desorption time was 240 min. The influence of the NaOH concentration in the desorption agent on the desorption rates for Mo and WO₃ was examined.

Figure 8 shows that when the concentration of NaOH in the desorption agent was ≥40 g/L, the Mo desorption rate was ≥99.35%, and the measured WO₃ desorption rate was ≥99.38%. When the NaOH solution was used as the desorption agent, the added amount of the desorption agent and the concentration of NaOH were controlled appropriately, and the Mo and WO₃ desorption rates were high. Therefore, the polyamine special resin was easy to desorb and showed good desorption performance.

The loaded and desorbed polyamine special resin samples prepared with the conditions described above were characterized with a Gemini Sigma 300/VP SEM. Figure 9 shows that the polyamine special resin statically adsorbed the sulfurized ammonium tungstate solution containing a high molybdenum content. In the loaded resin, the element contents from high to low were Mo (42.53%) > S (41.10%) > W (14.54%) > Na (1.83%), indicating that Mo and S were preferentially adsorbed (Mo was adsorbed by the polyamine special resin as MoO_xS_4−X²⁻). Na was introduced by the addition of a small amount of Na₂S when fine-tuning the S²⁻ concentration in the adsorption solution (ammonium tungstate solution). Na⁺ was not adsorbed by the special polyamine resin but was attached to the surface of the polyamine resin or inside the gap channels and was washed out with pure water.

Figure 10 shows that after the loaded polyamine special resin was desorbed by the NaOH solution, the element contents in the desorption resin from high to low were Na (97.56%) > S (2.28%) > W (0.16%) > Mo (0%). The tungsten and molybdenum adsorbed on the resin were fully desorbed, and the S remaining in the resin was removed in the regeneration process (composition of the regenerant; 5% hydrochloric acid and 1% H₂O₂). It was oxidized and removed to ensure cyclic adsorption by the polyamine special resin.

3.2. Dynamic Adsorption Tests

3.2.1. Dynamic Adsorption

The pretreated polyamine special resin (250 mL) was added to the simulated exchange column (the size of the simulated exchange column was φ 50 mm × 700 mm), and then the configured adsorption solution (ammonium tungstate molybdate sulfide solution, WO₃ 125.0 g/L, Mo 12.50 g/L, S²⁻ 14.65 g/L, CO₃²⁻ 0 g/L, pH 8.5) was added with a peristaltic pump; the flow was controlled at 2 mL/min, and the solution entered the simulated exchange column for adsorption. After being adsorbed by the resin, the feed solution was collected every 1 h, mixed, and sampled, and the concentrations of Mo and WO₃ were measured. When the Mo concentration in the adsorption solution collected from the simulated exchange column was ≥0.1 g/L, it was set as the molybdenum dynamic adsorption breakthrough adsorption capacity of the resin. At this time, adsorption was terminated, and the residual material solution in the simulated exchange column was washed out with 300 mL of pure water. The rate for the flow of the pure water into the exchange column was 5 mL/min. The washing water was collected, the volume was measured, the molybdenum and tungsten concentrations were measured, and the amounts of molybdenum and tungsten adsorbed were calculated.

Figure 11 shows that when the adsorption time was less than 6 h, molybdenum was adsorbed effectively, and the Mo concentration in the effluent after adsorption was less than 0.01 g/L. When the adsorption time was 9 h, the Mo concentration in the effluent after adsorption was 0.12 g/L, and the adsorption process was stopped for washing. The WO₃ concentration in the effluent after adsorption gradually increased with the longer adsorption times. After the adsorption time was ≥8 h, the WO₃ concentration in the effluent after adsorption was higher than that in the original adsorption solution, which was caused by iteration. At the initial stages of adsorption, there were many adsorption vacancies on the resin. After MoO_xS_4−X²⁻ (thiomolybdate) was preferentially adsorbed, some of WO₃ was also adsorbed. At the later stages of adsorption, as the number of adsorption vacancies on the resin decreased, MoO_xS_4−X²⁻ iterated the WO₃ previously adsorbed on the resin. After comprehensive adsorption of Mo and WO₃ from the effluent and washing water, the adsorption capacities of the resin for Mo and WO₃ were 53.48 mg/mL and 9.79 mg/mL, respectively, the adsorption rate of Mo was 99.05%, and the adsorption rate of WO₃ was 1.81%. The Mo adsorption rate = [1 − (Mo mass of adsorption effluent + Mo mass of washing water)/Mo mass of adsorption stock solution) × 100%, and the WO₃ adsorption rate = [1 − (adsorption effluent WO₃ mass + washing water WO₃ mass)/adsorption stock Mo mass) × 100%.

3.2.2. Dynamic Desorption

Dynamic desorption of the loaded polyamine special resin (the adsorption capacities of Mo and WO₃ on the loaded resin were 53.48 mg/mL and 9.79 mg/mL, respectively). Desorption strategy: For the first desorption, 500 mL of desorption agent was used. The concentration of NaOH was 45 g/L, the flow rate was 10 mL/min, and the desorption time was 240 min. After desorption was completed, the desorption solution was collected, the volume was measured, and molybdenum and tungsten levels were measured by sampling. For the second desorption, 500 mL of desorption agent was used. The concentration of NaOH was 45 g/L, the flow rate was 10 mL/min, and the desorption time was 120 min. After desorption was completed, the desorption solution was collected, the volume was measured, and molybdenum and tungsten levels were measured by sampling. After desorption, regenerative washing was conducted, and then the samples were prepared for the next test. Dynamic desorption: See

Table 1. The cascade of desorption data for the loaded resin.

NO.	Volume/mL	Concentration/(g·L−1)			Desorption Rate/%
		Mo	WO3	NaOH	Mo	WO3
First desorption	485	26.85	4.95	4.33	97.45	98.09
Second desorption	490	0.43	0.06	43.12	1.57	1.20

for the changes in Mo and WO₃ concentrations in the desorption solution.

Table 1 shows that after two cycles of desorption, the desorption rates of Mo and WO₃ reached 99.02% and 99.29%, respectively. The Mo concentration in the desorption solution after the first cycle reached 26.92 g/L, WO₃/Mo = 5.44/1, which was conducive to further utilization. The concentration of NaOH in the desorption solution after the second cycle reached 43.12 g/L, and this was used as the desorption agent in the next desorption cycle. The purpose was to reduce the consumption of the desorption agent and increase the Mo concentration in the desorption solution.

4. Conclusions

(1) The polyamine special resin was used to statically adsorb Mo from a sulfurized ammonium tungstate solution. Under the optimal conditions, the static adsorption capacities for Mo and WO₃ were 99.29 mg/mL and 31.97 mg/mL, respectively, and the desorption rates for Mo and WO₃ were 99.35% and 99.43%, respectively. EDS characterization of the loaded resin and the desorbed resin showed that the polyamine special resin had a high adsorption capacity for Mo and was easily desorbed with a NaOH solution.

(2) The dynamic adsorption tests of the polyamine special resin showed that for an ammonium tungstate solution containing WO₃ 125.0 g/L, Mo 12.50 g/L, S²⁻ 15.65 g/L and CO₃²⁻ 0 g/L, the adsorption capacities for Mo and WO₃ in dynamic adsorption by the polyamine special resin were 53.48 mg/mL and 9.79 mg/mL, respectively, and the adsorption rates for Mo and WO₃ were 99.05% and 1.81%, respectively. After dynamic adsorption, the loaded polyamine special resin was dynamically desorbed twice through the circulation of a 45 g/L NaOH solution. The desorption rates for Mo and WO₃ reached 99.02% and 99.29%, respectively, and the WO₃/Mo ratio in the desorption solution was 5.44/1.