La < 3 + >-doped lithium manganese oxide lithium ion sieve as well as preparation method and application thereof

Abstract

The invention discloses a La < 3 + >-doped lithium manganese oxide lithium ion sieve as well as a preparation method and application thereof, and belongs to the technical field of salt lake lithium extraction. The preparation method comprises the following steps: by taking Mn2O3 and LiOH as raw materials, carrying out hydrothermal reaction to generate LiMnO2, mixing the LiMnO2 with La2O3, grinding and calcining to form a La < 3 + >-doped spinel structure precursor La-LMO, and carrying out acid pickling to prepare La-HMO. La < 3 + > replaces part of Mn < 3 + >, the average valence state of manganese is improved, meanwhile, the structural stability of the manganese is enhanced through the high bond energy of La-O bonds, the number of exposed manganese atoms is reduced, manganese solution loss caused by Mn < 3 + > disproportionation reaction in the acid treatment process is effectively inhibited, the adsorbed oxygen content and active sites are increased, and the lithium ion adsorption capacity is remarkably improved. The material has high-selectivity adsorption capacity on lithium ions in salt lake brine in a strong alkaline environment, the manganese solution loss rate is obviously lower than that of traditional HMO, the cycle life is remarkably prolonged, and the industrial application potential is remarkably improved. The preparation process of the lithium ion sieve is simple, the raw material cost is low, and the technical bottlenecks that an existing manganese-based lithium ion sieve is poor in structural stability and high in manganese solution loss are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium extraction, and specifically relates to a La 3+ Doped lithium manganese oxide lithium ion sieve and its preparation method and application. Background Art

[0002] With the global energy transition toward clean energy and the rapid development of the new energy vehicle industry, lithium, as a key strategic resource of the 21st century, is becoming increasingly important. Due to its unique physical and chemical properties, lithium and its compounds demonstrate irreplaceable value in the new energy sector. Although the world's proven lithium reserves reach 89 million tons, of which over 62% reside in salt lake brines, its efficient development faces numerous technical obstacles. The lithium ion concentration in salt lake brines is relatively low, particularly in the numerous salt lakes of the Qinghai-Tibet Plateau, where the Mg / Li ratio is high and the brines coexist with a variety of high-concentration cations. Therefore, the development of a lithium extraction technology that is highly efficient, environmentally friendly, and economically viable is urgent.

[0003] Adsorption is a commonly used lithium extraction technology. Lithium ion sieve adsorbents mainly include three categories, namely aluminum-based lithium ion sieves (LiAl-LDHs), manganese-based lithium ion sieves (HMOs), and titanium-based lithium ion sieves (HTOs). In recent years, spinel-type HMOs have attracted much attention due to their large adsorption capacity, high adsorption selectivity, and excellent regeneration performance. The most studied HMO is H 1.6 Mn 1.6 O4, its theoretical adsorption capacity is 72.3 mg / g. However, due to the high Jahn-Teller effect, it is easy to spontaneously distort under the symmetrical geometric configuration to reduce the system energy, which faces severe challenges in practical applications. In addition, in Li 1.6 Mn 1.6 Manganese (Mn) in the O4 crystal structure is trivalent (Mn 3+ ) and tetravalent (Mn 4+ ) mixed valence. During the adsorbent acid treatment process, trivalent manganese (Mn 3+ ) can be easily disproportionated to form soluble divalent manganese (Mn 2+ ), which leads to manganese dissolution loss and subsequent structural distortion. In recent years, researchers have used methods such as surface modification, ion doping, morphology control and coating to improve the structural stability and cycling ability of HMO. Among these strategies, ion doping has been proven to be an effective means to regulate the material composition and crystal size. Existing doping includes: Na + , Ca 2+ Mg 2+ , K + 、S 2- 、Fe 3+ Although these doping increases the Li+ The adsorption capacity is still far from the theoretical adsorption capacity, and the manganese dissolution loss is still relatively high. Summary of the Invention

[0004] In order to overcome the disadvantages of the high dissolution rate of manganese in HMO in the prior art, which causes the poor structural stability and circulation capacity of HMO, the present invention aims to provide a La 3+ The doped manganese-based lithium ion sieve La-HMO not only improves the adsorption capacity but also effectively reduces the dissolution loss of manganese, thereby achieving improved HMO structural stability and cycle capacity.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: The first object of the present invention is to provide a La 3+ The preparation method of the doped lithium manganese oxide lithium ion sieve comprises the following steps: S1, mixing Mn2O3 with LiOH·H2O solution and stirring to carry out hydrothermal reaction. After the reaction is completed, filtering to obtain a solid product, and washing to obtain LiMnO2; S2, LiMnO2 and La2O3 were mixed with anhydrous ethanol and filtered, dried, ground and calcined to obtain La2O3 doped 3+ Lithium ion sieve precursor La-LMO; S3, doped with La 3+ The lithium ion sieve precursor La-LMO is acid-washed and dried to obtain La 3+ Doped lithium manganese oxide lithium ion sieve La-HMO.

[0006] Preferably, the Mn / Li molar ratio of Mn2O3 and LiOH·H2O in S1 is 1:2, and the concentration of the LiOH·H2O solution is 3~5 mol / L.

[0007] Preferably, the reaction temperature of the hydrothermal reaction in S1 is 100-150° C., and the reaction time is 45-55 h.

[0008] Preferably, the mass ratio of the amount ratio of LiMnO2 to La2O3 in S2 is 94: (3~17).

[0009] Preferably, the calcination temperature in S2 is 350-500° C., and the calcination time is 5-7 hours.

[0010] Preferably, in S3, HCl is used to acid-wash the La-LMO and filter it until the filtrate reaches neutrality.

[0011] The second object of the present invention is to provide La obtained by the above preparation method. 3+ Doped lithium manganese oxide lithium ion screen, the La 3+The doped lithium manganese oxide lithium ion sieve has a spinel structure.

[0012] Preferably, La 3+ The doping ratio is 2% to 10%, and the La 3+ Mn 3+ Doping substitution.

[0013] The third object of the present invention is to disclose the above-mentioned La 3+ Application of doped lithium manganese oxide lithium ion sieve in the adsorption of lithium ions in salt lake brine.

[0014] Preferably, the La 3+ Doped lithium manganese oxide lithium ion sieve undergoes lithium ion adsorption in a strongly alkaline environment.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The La 3+ The preparation method of the doped manganese-based lithium ion sieve La-HMO is to first prepare LiMnO2 by hydrothermal method using Mn2O3 and LiOH as raw materials, and then calcine with La2O3 and then acid-wash to obtain La-HMO. The raw material cost of the preparation of La-HMO proposed in the present invention is low, the preparation process is simple, the adsorption capacity of the prepared La-HMO for Li⁺ is significantly improved, and the Mn dissolution rate is significantly reduced. The lithium ion sieve is doped with La2O3 and La 3+ Replaced part of Mn 3+ , which increases the average valence of manganese in La-LMO. The increase in the average valence indicates that Mn 3+ The reduction of La content is beneficial to reduce manganese dissolution loss, and the lithium ion sieve still maintains the spinel structure. 3+ The doping of La promotes the growth of (100) crystal planes in the HMO spinel crystal structure, reducing the number of exposed manganese atoms. In addition, the bond energy of La-O bond (786.2 kJ / mol) is higher than that of Mn-O bond (402 kJ / mol), which further enhances the structural stability of HMO and its Li + The adsorption capacity of La-HMO is improved, and the dissolution loss of manganese is reduced by ion exchange between the lattices. Therefore, compared with HMO, the dissolution loss of La-HMO in adsorption / desorption is greatly reduced. 3+ It also increases the content of adsorbed oxygen in the material, thereby increasing the active sites and allowing more Li⁺ to be adsorbed. 3+ This not only improves the material's composition and lattice structure, but also increases the average oxidation state of Mn, fundamentally enhancing the stability of the framework structure. At the same time, doping increases the adsorbed oxygen content and improves the adsorption capacity.

[0016] The La 3+ La-H doped1.6 Mn 1.6 O4 lithium ion sieve, according to the adsorption experiment results, is effective in improving Li + While increasing the adsorption capacity, it also reduces the dissolution loss of manganese, which is of great significance for improving its cycle life in industrial applications and can be used for lithium extraction from salt lakes. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 XRD patterns of HMO prepared in the embodiment of the present invention and La-HMO with different doping ratios; Figure 2 Preparation of La in lithium ion sieve according to the embodiment of the present invention 3+ Relationship between doping ratio and I(400) / I(111) intensity; Figure 3 DES-mapping diagram of 2% doped La-HMO prepared in an embodiment of the present invention; (g) overall element distribution diagram; (h) O element distribution diagram; (i) Mn element distribution diagram; (j) La element distribution diagram Figure 4 SEM and TEM images of the lithium ion sieve prepared in the embodiment of the present invention, wherein (a) is the SEM image of HMO, (d) is the SEM image of 2% doped La-HMO, (bc) are TEM images of HMO, and (ef) are TEM images of 2% doped La-HMO; Figure 5 This is a graph showing the change in adsorption capacity of lithium ion sieves with different doping ratios prepared in an embodiment of the present invention over time; Figure 6 This is a graph showing the adsorption capacity changes of 2% doped La-HMO and HMO prepared in an embodiment of the present invention under different pH conditions; Figure 7 A comparison of the adsorption capacity of 2% doped La-HMO and HMO prepared in an embodiment of the present invention versus equilibrium concentration; Figure 8 The adsorption selectivity of 2% doped La-HMO in brine of Xitaijinaier Salt Lake prepared in the embodiment of the present invention is shown; Figure 9 This is an adsorption diagram of a 2% doped La-HMO adsorption / desorption cycle experiment prepared in an embodiment of the present invention; Figure 10 This is a diagram showing the Mn dissolution loss during the adsorption / desorption cycle experiment of 2% doped La-HMO prepared in an embodiment of the present invention; Figure 11 This is a morphology photo of La-HMO material. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0019] The present invention is described in further detail below with reference to the accompanying drawings: The present invention first discloses a method for La-storage of conventional lithium manganese oxide lithium ion sieve. 3+ Ion doping to prepare La 3+ The method of preparing a doped lithium manganese oxide lithium ion sieve (hereinafter referred to as La-HMO) specifically comprises the following steps: S1, mixing Mn2O3 with LiOH·H2O solution and stirring to carry out hydrothermal reaction. After the reaction is completed, filtering to obtain a solid product, and washing to obtain LiMnO2; S2, LiMnO2 and La2O3 were mixed, ground and calcined to obtain La-doped 3+ Lithium ion sieve precursor La-LMO; S3, doped with La 3+ The lithium ion sieve precursor La-LMO is acid-washed and dried to obtain La 3+ Doped lithium manganese oxide lithium ion sieve La-HMO.

[0020] Wherein, Mn2O3 is obtained by calcining MnCO3, specifically by calcining in air at 700℃~850℃ for 4~6 hours, that is, the calcination temperature can be 700℃, 720℃, 750℃, 780℃, 800℃, 830℃ or 850℃, preferably at 800℃, and the calcination time can be 4 hours, 4.2 hours, 4.5 hours, 4.8 hours, 5 hours, 5.2 hours, 5.5 hours, 5.8 hours or 6 hours. In some embodiments of the present invention, in step S1, the molar ratio of Mn to Li in the reactants is 1:2.

[0021] In some embodiments of the present invention, in step S1, the concentration of the LiOH·H2O solution is 3-5 mol / L, preferably 4 mol / L.

[0022] In some embodiments of the present invention, in step S1, the reaction temperature of the hydrothermal reaction is 100-150° C., and the reaction time is 45-55 h, preferably at 120° C. for 48 h.

[0023] In some embodiments of the present invention, the mass ratio of LiMnO2 to La2O3 in step S2 is 94: (3-17), that is, the molar amount of La in the reactants is 2%-10% of the molar amount of Mn.

[0024] In some embodiments of the present invention, the calcination temperature in step S2 is 350-500° C., and the calcination time is 5-7 hours, preferably calcined at 400° C. for 6 hours.

[0025] In some embodiments of the present invention, HCl is used to pickle the La-LMO in step S3, wherein the concentration of HCl is 0.5 mol / L.

[0026] The embodiment of the present invention discloses La-HMO, which is a spinel structure of the lithium ion sieve. 3+ The Mn in the spinel structure of traditional lithium manganese oxide lithium ion sieve 3+ The sites are doped and replaced with a ratio of 2% to 10%.

[0027] The embodiments of the present invention also disclose the application of La-HMO in the adsorption of lithium ions in salt lake brine. The La-HMO can show a certain lithium ion adsorption effect in solutions with pH values ranging from 6 to 12, and the adsorption effect is better under strong alkaline conditions.

[0028] The following is a detailed description with reference to the embodiments.

[0029] The following examples were performed using conventional equipment in the art. Unless otherwise specified, all raw materials and reagents used were commercially available products with specifications conventional in the art, or they can be prepared or formulated by known methods or reagent instructions. Experimental procedures in the following examples, where specific conditions are not specified, generally followed conventional conditions or those recommended by the manufacturer.

[0030] Example 1 First, a certain amount of MnCO3 was calcined in air at 800°C for 5 hours to obtain Mn2O3 solid.

[0031] Next, 10 g of Mn2O3 solid was weighed and mixed with 64 mL of a 4 mol / L LiOH·H2O solution in a Teflon-lined container. The mixture was thoroughly stirred and transferred to an autoclave. The reaction was continued at 120°C for 48 hours. After cooling naturally, the solid product was filtered to obtain a solid product. The solid product was repeatedly washed with deionized water until the residual liquid was neutral. The solid product was then dried at 60°C to obtain LiMnO2.

[0032] Then, 5 g of LiMnO2 and 0.1735 g of La2O3 were mixed, ground thoroughly, and calcined in a muffle furnace at 400 °C for 6 h to obtain La-LMO.

[0033] Disperse 2 g of La-LMO in 200 mL of 0.5 mol / L HCl solution, stir for 12 hours, and filter until the filtrate reaches neutrality. The resulting solid product is then dried at 60°C overnight. This yields La-HMO with a 2% doping ratio.

[0034] Example 2 First, a certain amount of MnCO3 was calcined in air at 800°C for 5 hours to obtain Mn2O3 solid.

[0035] Next, 10 g of Mn2O3 solid was weighed and mixed with 64 mL of a 4 mol / L LiOH·H2O solution in a Teflon-lined container. The mixture was thoroughly stirred and transferred to an autoclave. The reaction was continued at 120°C for 48 hours. After cooling, the solid product was filtered to obtain a solid product. The solid product was repeatedly washed with deionized water until the residual liquid was neutral. The solid product was then dried at 60°C to obtain LiMnO2.

[0036] Then, 5 g of LiMnO2 and 0.4338 g of La2O3 were mixed and stirred using anhydrous ethanol as a dispersant, filtered, dried, fully ground, and calcined in a muffle furnace at 400°C for 6 hours to obtain La-LMO.

[0037] 2 g of La-LMO was dispersed in 200 mL of 0.5 mol / L HCl solution and stirred for 12 hours before filtration until the filtrate reached neutrality. The resulting solid product was then dried at 60°C overnight to obtain La-HMO with a doping ratio of 5%.

[0038] Example 3 First, a certain amount of MnCO3 was calcined in air at 800°C for 5 hours to obtain Mn2O3 solid.

[0039] Next, 10 g of Mn2O3 solid was weighed and mixed with 64 mL of a 4 mol / L LiOH·H2O solution in a Teflon-lined container. The mixture was stirred thoroughly to form a mixture. The mixture was transferred to an autoclave and reacted at 120°C for 48 hours. After cooling naturally, the solid product was filtered to obtain a solid product. The solid product was repeatedly washed with deionized water until the residual liquid was neutral. The solid product was then dried at 60°C to obtain LiMnO2.

[0040] Then, 5 g of LiMnO2 was mixed with 0.8675 g of La2O3, ground thoroughly, and calcined in a muffle furnace at 400 °C for 6 h to obtain La-LMO.

[0041] 2 g of La-LMO was dispersed in 200 mL of 0.5 mol / L HCl solution and stirred for 12 hours before filtration until the filtrate reached neutrality. The resulting solid product was then dried at 60°C overnight to obtain La-HMO with a doping ratio of 10%.

[0042] Different ratios of La doped LMO were used to adsorb Li + Experiment, from Li + From the perspective of adsorption capacity, 2% doping has the highest adsorption capacity, and XRD analysis was performed on materials doped with different proportions.

[0043] Test Example 1 The adsorption of Li by HMO doped with La at different ratios was carried out. + experiment.

[0044] 0.05 g of 2%-La-HMO, 5%-La-HMO, and 10%-La-HMO were added to a 100 mg / L LiCl solution, respectively. The mixture was shaken at 25°C. Samples were taken at different times and filtered through a 0.22 μm filter membrane to obtain clear solutions. The ion concentration was measured by AAS, and the adsorption capacity was calculated.

[0045] The results are as follows Figure 5 As shown, the adsorption capacity of 2% doping is stable and the highest. At the same time, XRD analysis of materials doped with different proportions was carried out to explore the changes in the crystal surface.

[0046] The results are as follows Figure 1 As shown in Figure 2, doping does not change the spinel structure of the lithium ion sieve. Figure 2 As shown in Figure 2, the intensity of (400) and (111) crystal planes with different doping ratios are compared. When the doping ratio is 2%, the (400) crystal plane grows preferentially, which is beneficial to reduce the exposure of Mn atoms. Figure 3 DES results show that Mn, O, and La in 2% doped La-HMO are uniformly distributed in the material. Figure 4 The SEM results show that the microstructures of 2% doped La-HMO and HMO are both blocky particle aggregations, and the lattice fringe spacing of the samples in TEM analysis is 0.46 nm, which corresponds well to the spinel HMO phase (111) crystal plane determined by XRD analysis. Comprehensive analysis, 2% La 3+ The doping ratio is the most suitable, and the structure of the manganese-based lithium ion sieve is not changed. The photo of the prepared La-HMO product is shown in Figure 11 , with a typical adsorbent appearance.

[0047] Test Example 2 To explore the optimal adsorption pH value.

[0048] Take 50 mL of LiCl solution with pH = 6, 8, 9, 10, 11, and 12. Take two groups of LiCl for each pH value. Add 0.05 g of undoped La-HMO adsorbent and 2% doped La-HMO to these two groups, respectively. Oscillate at 25°C for 10 h, and take samples to calculate the adsorption capacity.

[0049] The results are as follows Figure 6 As shown in the figure, at pH = 6, the adsorption capacity of HMO and 2% doped La-HMO is 2.6 mg / g. When the pH is increased to 12, the adsorption capacity of HMO and 2% doped La-HMO is 24.00 mg / g and 29.2 mg / g, respectively. This shows that the strong alkaline environment is more suitable for Li + The adsorption capacity of 2%-La-HMO is greater than that of undoped HMO.

[0050] Test Example 3 The adsorption capacity at different equilibrium concentrations was investigated.

[0051] Take 2 groups of 50 mL of Li solution with initial concentrations of 20, 40, 60, 80, and 100 mg / L respectively. + The solution was added with 0.05 g HMO and 2%-La-HMO adsorbent respectively, and the mixture was shaken at 25 °C for 10 h. After the reaction was completed, samples were taken to detect Li + concentration, calculate the equilibrium concentration and adsorption capacity.

[0052] The results are as follows Figure 7 As shown, the adsorption capacity increases with the + The adsorption capacity of 2%-La-HMO is always greater than that of HMO. + At an equilibrium concentration of 90 mg / L, the adsorption capacities of 2%-La-HMO and HMO reached their maximum values, reaching 35.4 mg / g and 33.6 mg / g, respectively. This indicates that at different equilibrium concentrations, the adsorption capacity of 2%-La-HMO is greater than that of undoped HMO.

[0053] Test Example 4 Selective adsorption experiments were carried out using brine from Xitaijinaier Salt Lake.

[0054] The composition of the brine from Xitaijinaier Salt Lake used in the test is shown in the table below:

[0055] 0.05 g of 2% doped La-HMO prepared in Example 1 was added to 50 mL of Xitaijinaier Salt Lake brine and LiCl solution respectively for comparison. The mixture was shaken at 25°C for 10 h, and samples were taken to measure the concentrations of different ions. The results are shown in Figure 8 middle.

[0056] As can be seen from the figure, in actual brines with high Mg / Li ratios, such as the brine from the Xitaijinaier Salt Lake, 2% doped La-HMO has a good adsorption capacity, with a small but not significant difference compared to the prepared LiCl solution. Furthermore, it exhibits good selectivity for lithium ions in complex environments.

[0057] Test Example 5 Adsorption / desorption cycle experiments.

[0058] To La 3+ The doped La-HMO undergoes 5 cycles of adsorption / desorption of Li + Cycle experiment.

[0059] 0.05 g of the 2% doped La-HMO and undoped HMO prepared in Example 1 were added to a 100 mg / L LiCl solution, shaken for 10 h, and sampled. The solid was filtered and dried, then acid-washed with 0.5 mol / L HCl for 12 h, filtered, and adsorbed again. The above steps were repeated for a cycle experiment.

[0060] The experimental results are as follows Figure 9 , Figure 10 As shown in Figure 3, the La-HMO adsorption capacity decay is slow and higher than that of undoped HMO. After five cycles, the adsorption capacity of 2% doped La-HMO can still be maintained at 33.10 mg / g.

[0061] The Mn dissolution loss in 2% doped La-HMO decreased from 4.62% to 4.04% during 5 cycles, which was lower than that of undoped HMO (4.87%→4.65%), indicating that La doping reduced the Mn dissolution loss.

[0062] The above content is only for explaining the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A La 3+ The method for preparing doped lithium manganese oxide lithium ion sieve is characterized in that: The following steps are involved: S1, mixing Mn2O3 with LiOH·H2O solution and stirring to carry out hydrothermal reaction. After the reaction is completed, filtering to obtain a solid product, and washing to obtain LiMnO2; S2, LiMnO2 and La2O3 were mixed with anhydrous ethanol and filtered, dried, ground and calcined to obtain La2O3 doped 3+ Lithium ion sieve precursor La-LMO; S3, doped with La 3+ The lithium ion sieve precursor La-LMO is acid-washed and dried to obtain La 3+ Doped lithium manganese oxide lithium ion sieve La-HMO.

2. La according to claim 1 3+ The method for preparing doped lithium manganese oxide lithium ion sieve is characterized in that: The Mn / Li molar ratio of Mn2O3 and LiOH·H2O described in S1 is 1:2, and the concentration of the LiOH·H2O solution is 3~5 mol / L.

3. La according to claim 1 3+ The method for preparing doped lithium manganese oxide lithium ion sieve is characterized in that: The reaction temperature of the hydrothermal reaction in S1 is 100-150° C., and the reaction time is 45-55 h.

4. La according to claim 1 3+ The method for preparing doped lithium manganese oxide lithium ion sieve is characterized in that: The mass ratio of LiMnO2 to La2O3 described in S2 is 94: (3~17).

5. La according to claim 1 3+ The method for preparing doped lithium manganese oxide lithium ion sieve is characterized in that: The calcination temperature in S2 is 350-500° C., and the calcination time is 5-7 hours.

6. La according to claim 1 3+ The method for preparing doped lithium manganese oxide lithium ion sieve is characterized in that: In S3, HCl is used to acid-wash and filter the La-LMO until the filtrate reaches neutrality.

7. A La 3+ Doped lithium manganese oxide lithium ion sieve, characterized in that Prepared by the preparation method according to any one of claims 1 to 7.

8. La according to claim 7 3+ Doped lithium manganese oxide lithium ion sieve, characterized in that The La 3+ The doping ratio is 2% to 10%, and the La 3+ Mn 3+ Doping substitution.

9. La according to claim 7 or claim 8 3+ Application of doped lithium manganese oxide lithium ion sieve in the adsorption of lithium ions in salt lake brine.

10. La according to claim 9 3+ The application of doped lithium manganese oxide lithium ion sieve in adsorbing lithium ions in salt lake brine is characterized by: Lithium ion adsorption occurs in a strongly alkaline environment.

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