Chloride Leach Solution Research Articles

The uptake of silver(I) from chloride solutions by amine extractants

The amine extractants, bis(2-ethylhexyl)amine, N,N-dimethylethanolamine, and trioctylamine were used to recover silver(I) ions from chloride solutions. The effect of the pH, contact time, extractant concentration and reextraction were studied. It was found that extraction of silver(I) depended on the pH, extractant concentration and strongly on the contact time. Reextraction of Ag(I) ions from the loaded organic phase showed that the metal can be removed in over 50% for the three extractant using sodium hydroxide. The recovery of silver from the chloride leaching solutions were above 85% for bis(2-ethylhexyl)amine, above 58% for N,N-dimethylethanolamine, and above 70% for trioctylamine.

Comparing iron phosphate and hematite precipitation processes for iron removal from chloride leach solutions

The presence of iron in pregnant leach solutions presents significant processing challenges. The removal of iron impurities from leach solutions by means of iron phosphate precipitation may be a feasible alternative to more conventional iron oxide/iron hydroxide precipitation processes. This study compares the performance of the iron phosphate precipitation process with that of the hematite process at different operating temperatures (40°C–90°C), pH conditions (pH 1–pH 3) and seeding measures for the removal of iron from a chloride leach solution. The extent of iron removal, co-precipitation of nickel and copper, and solid-liquid separation were used as performance criteria for the comparison.Seeded iron phosphate precipitation at pH 1 and 40°C resulted in 98.8% iron removal with 0.5% nickel and 2.8% copper losses. 99.8% iron removal was achieved with the iron phosphate precipitation process at pH 1 and 80°C, but the nickel and copper losses increased to 8.7% and 20.8%, respectively, with the increase in temperature. Seeded hematite precipitation at pH 1 and 80°C yielded 99.6% iron removal with 3.5% nickel and 1.7% copper losses. For the hematite process, nickel and copper losses decreased with an increase in temperature. Increasing the pH yielded higher nickel and copper losses for both processes.All seeded precipitation experiments produced easily filterable precipitates. Unseeded iron phosphate precipitates produced at 40°C and pH 1 were filterable, but increased nickel and copper losses were observed. Unseeded hematite precipitation resulted in high nickel and copper losses, with the precipitates practically impossible to filter. Iron phosphate precipitates exhibited more favourable settling characteristics than the precipitate produced with the hematite process.

Separation of cobalt and nickel from chloride leach solution of nickel laterite ore by solvent extraction

In order to separate Ni and Co from the chloride leach solution of laterite ores with high Fe content, solvent extraction and stripping experiments were performed. Various extractants, such as cationic extractants (Cyanex 272 (di(2,4,4-trimethylpentyl)phosphinic acid)), D2EHPA (di-2-ethylhexyl phosphoric acid), Versatic 10 (a carboxylic acid), amine extractants (Alamine 336 (tri-octyl/dodecyl amine), Aliquat 336 (a mixture of tri-octyl/decyl ammonium chloride), etc.), and neutral extractant (TBP (tri-butyl phosphate)) have been tested. Most of the Co together with some amount of Fe and Mn was extracted by Aliquat 336. The purified Co solution was obtained by extraction with Cyanex 301 (dialky1dithiophosphinic acid) after stripping the loaded Aliquat 336. Extraction of the filtrate with saponified Versatic 10 after precipitation of Al resulted in the separation of Ni and Mn from Ca and Mg. Ni was then selectively stripped by H2SO4 solution. The nickel solution with 99% purity was obtained from the batch simulation experiments.

Separation of Pr and Nd from La in chloride solution by extraction with a mixture of Cyanex 272 and Alamine 336

The possibility of separation of Pr and Nd from La in a chloride leaching solution of monazite sand has been investigated by using a binary mixture of Cyanex 272 (bis(2,4,4-trimethylpentyl) phosphinic acid) and Alamine 336 (tri-octyl/decyl amine). The binary mixture showed synergism on the extraction of the three metals and led to an increase in the separation factor between Pr/Nd and La compared to Cyanex 272 alone. Although the addition of chloride ion into aqueous increased the extraction of the metals, this addition had negative effect on the separation of Nd/Pr and La. McCabe-Thiele diagrams for the extraction of Pr and Nd with the binary mixture were constructed. Stripping of metals from the loaded organic phase was achieved with 0.7 M HCl. The difference in the solvent extraction of the rare earth elements from chloride solution between the binary mixture and saponified extractants was also discussed.

Recovery of nickel, cobalt, copper and zinc in sulphate and chloride solutions using synergistic solvent extraction

A number of synergistic solvent extraction (SSX) systems have been developed to recover nickel, cobalt, zinc and copper from sulphuric and chloride leach solutions by the solvent extraction team of CSIRO, Australia. These include (1) Versatic 10/CLX50 system for the separation of Ni from Ca in sulphate solutions, (2) Versatic 10/4PC system for the separation of Ni and Co from Mn/Mg/Ca in sulphate solutions, (3) Cyanex 471X/HRJ-4277 system for the separation of Zn from Cd in sulphate solutions, (4) Versatic 10/LIX63 system for the separation of Co from Mn/Mg/Ca in sulphate solutions, (5) Versatic 10/LIX63/TBP system for separation of Ni and Co from Mn/Mg/Ca in sulphate solutions, (6) Versatic 10/LIX63 system for the separation of cobalt from nickel in sulphate solutions by difference in kinetics, (7) Cyanex 272/LIX84 system for the separation of Cu/Fe/Zn from Ni/Co in sulphate solutions, (8) Versatic 10/LIX63/TBP system to recover Cu/Ni from strong chloride solutions, and (9) Versatic 10/LIX63 system to separate Cu from Fe in strong chloride solutions.The synergistic effect on metal separation and efficiency is presented and possible industrial applications are demonstrated. The chemical stability of selected SSX systems is also reported.

Separation of Co and Ni from a chloride leach solutions of laterite ore by solvent extraction with extractant mixtures

In order to separate Ni(II) and Co(II) from the chloride leaching solution of nickel laterite ore, solvent extraction experiments with the mixtures of organophosphorus extractants and LIX63 were performed in the pH range from 1 to 3. Among the studied mixtures, a mixture of D2EHPA and LIX63 with the molar ratio of 3:7 showed the best efficiency for the selective extraction of Ni (62%) and Co (96%) from Al and other impurities. High concentration of HCl or H2SO4 could strip Ni from the loaded mixture, while Co was preferentially stripped by low concentration of the acids.

Recovery of Platinum from Chloride Leaching Solutions of Spent Reforming Catalysts by Ion Exchange

Platinum and base metals (Al, Fe, Si) are present in the chloride leaching solutions of spent reforming catalysts. In order to develop a process to recover platinum from such leaching solutions, batch and continuous ion exchange experiments were performed using a strong anionic resin (DiaionSA10AP). The adsorption equilibrium data of Pt are described by the Langmuir adsorption isotherm. Batch experiments indicate that it is possible to separate Pt and Fe from other metal ions in the present leaching solution. Fe was selectively removed from the loaded resin using diluted HCl, while Pt was eluted using thiourea after Fe removal. The results of column experiments verified the feasibility of the separation and recovery of platinum from leaching solutions using the present process. The elution efficiency exceeded 99% for both Pt and Fe. The recovery percentage of Pt from the leaching solution using this method was 99.3%. [doi:10.2320/matertrans.M2015027]

Recovery of platinum, palladium and rhodium from acidic chloride leach solution using ion exchange resins

The objective of this study was to investigate the applicability and performance of the selected ion exchangers with different physicochemical characteristics and functional groups to simultaneously recover three different platinum group elements (PGE), platinum(IV), palladium(II) and rhodium(III), present in a chloride solution produced by the leaching of spent automotive catalysts. The tested ion exchangers included a resin with a quaternary ammonium functional group (Lewatit MonoPlus (M+) MP 600), a resin with a polyamine functional group (Purolite S985) and a resin with a thiouronium functional group (XUS 43600.00). The study also focused on the achievable desorption from the loaded resins using different eluent systems. The leach solution was chlorine-saturated and contained 2.35mol/L hydrochloric acid, platinum and palladium in concentrations of 0.13mmol/L, and rhodium 0.03mmol/L. It was found that XUS 43600.00 showed the best adsorption performance for platinum(IV) and palladium(II) chloride complexes among the investigated resins, but weak affinity for rhodium(III) chloride complexes was observed for all three resins. The adsorption kinetics were found to obey the Ho pseudo-second order expression. For Lewatit MonoPlus (M+) MP 600 and Purolite S985 the adsorption was best described by the Freundlich isotherm, while for XUS 43600.00 the Langmuir isotherm was more apt. Desorption of the PGE was examined using four different elution agents: sodium thiocyanate (2mol/L), hydrochloric acid (2mol/L), thiourea (1mol/L) in hydrochloric acid (2mol/L), and thiourea (1mol/L) in sodium hydroxide (2mol/L). The results showed that platinum and palladium can be fully eluted with the acidic thiourea but desorption of rhodium proved difficult with all the eluents.

Separation of Ce and La from Synthetic Chloride Leach Solution of Monazite Sand by Precipitation and Solvent Extraction

Precipitation and solvent extraction experiments have been performed to recover light rare earths from simulated monazite sand chloride leach solutions. Precipitation conditions were obtained to recover Ce by adding NaClO as an oxidant. Among some cationic extractants (PC 88A, D2EHPA, Cyanex 272, LIX 63), PC 88A showed the best performance to separate La from the resulting chloride solution. Furthermore, the mixture of PC 88A with other solvating (TBP, TOPO) and amine extractants (Alamine 336, Aliquat 336) was tested to increase the separation factor of La from Pr and Nd. The use of mixed extractants greatly enhanced the separation of La from the two other metals. McCabe–Thiele diagrams for the extraction of Pr and Nd with the PC 88A/Alamine 336 mixture were constructed.

염산용액에서 유기인산계 추출제에 의한 Nd와 Pr의 분리추출

Abstract Solvent extraction experiments have been performed to separate Nd and Pr from chloride leaching solution of monazite sandusing single Cyanex272 and mixed extractants as PC88A+Cyanex272 and PC88A+TBP. For this purpose, the effect of the con-centration of extractants on the extraction and separation of the two metals were studied by varying the pH of aqueous solution.In the experimental ranges conducted in this study, the distribution coefficients of Nd were higher than those of Pr. In Cyanex272system, our results indicated that concentration of extractant and initial pH did not affect distribution coefficients, but separationfactor was increased with increasing initial pH. In binary extractant system, distribution coefficients were lower than those ofsingle PC88A system, whereas separation factor was similar in both mixed and single extractant system.Key words : solvent extraction, Cyanex272, NdCl 3 , PrCl 3 , separation * Received : February 4, 2014 · Revised : March 5, 2014 · Accepted : March 18, 2014Corresponding Author : Man-Seung Lee (E-mail : mslee@mokpo.ac.kr)Department of Advanced Materials Science & Engineering, Mokpo National University, 61 Dorim-ri, Chungkye-myun, Muan-gun,Chonnam, 534-729, KoreaTel : +82-62-450-2492 / Fax : +82-62-450-2498 ⓒThe Korean Institute of Resources Recycling. All rights reserved. This is an open-access article distributed under the termsof the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/), which permitsunrestricted non-commercial use, distribution and reproduction in any medium, provided the original work is properly cited.

Fe(III) removal from a synthetic chloride leach solution of nickel laterite by N,N–diethyldodecanamide

In recent years, leaching with chloride solutions has attracted much interest for nickel laterite processing due to its high leaching rate, fast kinetics and the recycling of lixiviant and HCl. However, the presence of large amounts of Fe(III) in the pregnant leach solution becomes a big challenge for the recovery of nickel and cobalt.A solvent extraction (SX) method using N,N-diethyldodecanamide (DEDA) to remove Fe(III) from a synthetic chloride leach solution of nickel laterites was investigated. It was found that using an organic system consisting of 30% (v/v) DEDOA and 30% (v/v) isodecanol (as phase modifier), over 90% Fe(III) was extracted from the strong chloride solution (6M Cl) in a single contact and high selectivity of Fe(III) over other metals was obtained in the pH range tested. The Fe(III) extraction increased substantially with the increase in chloride concentration. High Fe(III) stripping efficiency was obtained using water. The Fe(III) extraction McCabe–Thiele diagram shows that almost all Fe(III) can be extracted using three stages at an A/O ratio of 1.25:1. The Fe(III) stripping McCabe–Thiele diagram shows that almost all Fe(III) can be stripped using two stages at an O/A ratio of 2:1. Extraction and stripping kinetics were very fast and phase separation was good and fast for practical operation.

모나자이트 샌드의 염산침출용액으로부터 용매추출에 의한 Nd와 Pr의 분리

Abstract Solvent extraction experiments have been performed to separate Nd and Pr from chloride leaching solution of monazite sandusing PC88A and D2EHPA. For this purpose, the effect of the saponification of PC88A and D2EHPA on the extraction and sep-aration of the two metals were studied by varying the pH of aqueous solution. In the experimental ranges conducted in this study,the distribution coefficients of Nd were higher than those of Pr and separation factor value increased with the increase of solutionpH. Saponification of PC88A enhanced the distribution coefficients of Nd and Pr as well as the separation factor. Saponificationof D2EHPA had some effect on the extraction of the two metals but little effect on the separation factor.Key words : Solvent extraction, PC88A, D2EHPA, Saponification, Separation *Received : August 19, 2013 · Revised : September 9, 2013 · Accepted : September 23, 2013Corresponding Author : Man-Seung Lee (E-mail : mslee@mokpo.ac.kr)Department of Advanced Materials Science & Engineering, Mokpo National University, 61 Dorim-ri, Chungkye-myun, Muan-gun,Chonnam, 534-729, KoreaTel : +82-62-450-2492 / Fax : +82-62-450-2498 ⓒThe Korean Institute of Resources Recycling. All rights reserved. This is an open-access article distributed under the termsof the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/), which permitsunrestricted non-commercial use, distribution and reproduction in any medium, provided the original work is properly cited.

Removal of Mo and Fe from the Cobalt Chloride Solution by Ion Exchange during the Recovery Process from Spent Hydrodesulfurization Catalysts

During the recovery of cobalt from the chloride leaching solutions of spent hydrodesulfurization catalysts by solvent extraction with amine, a cobalt chloride solution of ∼98% purity was obtained by stripping of the loaded amine with HCl solution. The major impurity elements in this cobalt chloride solution were molybdenum and iron, whose concentration was <10 ppm. In order to remove these impurities from the solution, ion exchange experiments have been performed. For this purpose, strong cationic (Diphonix) and anionic exchange resins (AG1-x8) were tested in the pH range from zero to 4. Our results indicated that Mo and Fe were removed simultaneously by ion exchange with Diphonix from the solution with pH 1. The loading capacity of Diphonix for Mo and Fe at this pH was found to be 90 and 40 mg/g of resin. Column experiments verified that pure cobalt chloride solution with 99.97% purity was obtained by ion exchange with Diphonix.

Recovery of HCl from Chloride Leach Solution of Spent HDS Catalyst by Solvent Extraction

Abstract In the present work, amine based extractant and its mixture with cationic and solvating extractants were tested for the extraction of HCl from chloride solution containing Al(III). The chloride feed solution resulted from the leaching of spent HDS (hydro-desulfurization) catalysts. For this purpose, amine extractants, such as TOA (trioctyl amine), Alamine 336 (a mixture of tri-octyl/decyl amine), Alamine 308 (tri-isooctyl amine), and TEHA (tri 2-ethylhexyl amine) were used and the extraction and stripping behavior of HCl was compared. The extracted HCl was easily stripped from loaded TEHA phase, when compared with the other tested tertiary amine system. Solvent extraction reaction of HCl by TEHA was determined from the extraction data. Unlike TOA and Alamine 336, adding cationic extractant to TEHA had negligible effect on the extraction and stripping of HCl. In our experimental ranges, no Al was extracted by amines and pure HCl was recovered. MaCabe- Thiele diagrams for the extraction and stripping of HCl by TEHA were constructed.

Microfluidic solvent extraction of platinum and palladium from a chloride leach solution using Alamine 336

Microfluidic solvent extraction (μSX) of platinum and palladium from chloride leach solution using Alamine 336 had been conducted. The leach solution was produced by leaching of spent automotive catalysts. A microfluidic Y–Y channel embedded in a Pyrex™ microchip was used as the extraction system. Platinum and palladium extractions (>99%) occurred at μSX contact time as fast as 1s with subsequent marginal extraction efficiency increases for longer contact times with comparable extraction performance to that of bulk SX. Findings from this preliminary study are useful in initiating a new metallurgical technique in the field of recovering precious (high-value) metals present in low concentrations which are otherwise not technically amenable (or economically viable) to extraction using current conventional methods.

Solvent Extraction Separation of Mo and Co from Chloride Solution Containing Al

Solvent extraction studies were carried out to investigate the selectivity of some extractants towards Mo and Co from synthetic acidic chloride leach solution of spent HDS catalyst. The composition of the synthetic solution was (in ppm): Mo-394, Co-119, Al-1782 and 3kmol/m 3 of HCl. Among the several solvating and amine extractants that were tested, TOPO and Alamine 308 showed some potential towards the extraction of Mo and Co, respectively. The reasons for this greater extraction tendency of the corresponding extractants were also described thoroughly. Furthermore, the separation of Co and Al was investigated by varying the concentration of HCl. Finally, a possible extraction system for the separation of Mo and Co was presented. Our results can be utilized in developing a process for the recovery of Mo and Co from spent catalysts. [doi:10.2320/matertrans.M2012287]

Separation and recovery of copper, nickel, cobalt and zinc in chloride solutions by synergistic solvent extraction

The synergistic solvent extraction (SSX) system consisting of LIX63, Versatic 10 and TBP in Shellsol D70 can be used to separate copper, nickel, cobalt and zinc from strong chloride solutions and to transfer copper and nickel to sulphate media for electrowinning.In the first circuit with the SSX system, over 95% Cu was extracted after a single contact, with the co-extraction of some 12% Ni and negligible Co, Mn and Ca. The loaded organic solution could be scrubbed using water to produce the loaded strip liquor suitable for copper conventional electrowinning. In the second circuit with an SX system consisting of Alamine 336 and TBP in Shellsol D70, over 99% Zn, 87% Co and 43% Mn were extracted at pH 3.5 from the copper depleted raffinate after a single contact. The co-extraction of Ni and Ca was negligible. After stripping, the zinc, cobalt and manganese in the loaded strip liquor could be separated from each other using conventional solvent extraction or ion exchange techniques. In the third circuit for nickel with the same SSX system, over 98% Ni was extracted from the copper–cobalt–zinc depleted raffinate in a single contact. The co-extraction of chloride, manganese and calcium was small and was scrubbed. After stripping using spent nickel electrolyte, the loaded strip liquor would be suitable for conventional electrowinning. The nickel extraction and stripping kinetics were reasonably fast for industrial operation. A process flowsheet to recover copper, cobalt, zinc and nickel from strong chloride leach solutions has been proposed.

RECOVERY OF COPPER FROMAMASSIVE POLYMETALLIC SULPHIDE BY HIGH CONCENTRATION CHLORIDE LEACHING

A new process for the recovery of copper and associated base metals from a polymetallic massive sulphide ore is described. The massive sulphide contains copper and especially nickel sulphide in a mineralogical form which negates both good recovery and high grades in concentrates using conventional flotation methods. Utilizing the properties of high concentration chloride brines, a hydrometallurgical flowsheet has been developed and tested whereby the recovery of all of the metals and some of the power requirements for the plant itself can be derived from the ore. The new process involves leaching of the whole ore in two stages: 1) a primary leach during which the pyrrhotite is leached with HCl assisted by MgCl2 to yield hydrogen sulphide (from which energy is produced) and 2) a ferrous chloride solution; a secondary ferric chloride/MgCl2 oxidizing leach during which the economic metals (C, Ni and Co) are solubilized. The generated primary ferrous chloride leach solution is subjected to oxidation and hydrolytic decomposition to precipitate the excess iron as hematite and regenerate the HCl lixiviant. Copper recovery is effected via ion exchange and generation of a copper sulphate electrolyte advanced to conventional electrowinning. The Ferguson Lake deposit of Starfield Resources Inc. in Nunavut, Canada, is the subject of this paper, which focuses on the leaching and copper recovery unit operations of the proposed flowsheet.On decrit un nouveau procede pour la recuperation du cuivre et des metaux de base associes d’un minerai polymetallique massif de sulfure. Le sulfure massif contient du cuivre et surtout du sulfure de nickel sous une forme mineralogique qui empeche a la fois une bonne recuperation et des teneurs elevees dans les concentres lorsqu’on utilise les methodes conventionnelles de flottation. Utilisant les proprietes de saumures de chlorure a concentration elevee, on a developpe et evalue un schema de procede d’hydrometallurgie par lequel on peut deriver, a partir du minerai, la recuperation de tous les metaux et une partie de l’energie necessaire pour l’usine meme. Le nouveau procede implique la lixiviation du minerai entier en deux etapes: 1) un lessivage primaire durant lequel la pyrrhotine est lessivee avec du HCl assiste deMgCl2 pour produire de l’acide hydrosulfurique (a partir duquel on produit de l’energie) et 2) une solution de chlorure ferreux; un lessivage oxydant secondaire de chlorure ferrique/MgCl2 lors duquel on solubilise les metaux economiques (C, Ni et Co). La solution de lessivage primaire generee de chlorure ferreux est soumise a une oxydation et une decomposition hydrolytique pour precipiter l’exces de fer en hematite et pour regenerer le lixiviat HCl. La recuperation du cuivre est effectuee via l’echange d’ions et la production d’un electrolyte de sulfate de cuivre, avancee a l’electro-obtention conventionnelle. Le depot de Ferguson Lake de Starfield Resources Inc. au Nunavut, Canada, est le sujet de cet article, lequel se concentre sur les unites d’operation de lixiviation et de recuperation du cuivre du schema de procede propose.

Kinetic Study on the Leaching of Pt, Pd and Rh from Automotive Catalyst Residue by Using Chloride Solutions

Recycling platinum group metals (PGMs) from waste and/or secondary resources is becoming quite important due to the limitation of the natural resource deposits of PGMs. Among the processes of PGMs’ recycling from secondary resources, the hydrometallurgical method draws extensive concerns, particularly for the selection of leaching solution. The present work evaluated the ability of chloride leaching solutions, i.e. HCl–H2O2 and NaClO–HCl–H2O2 to extract Pt, Pd and Rh from a kinetic point of view. The effect of temperature in the range of 277–307 K and time were also examined under the conditions of −500 μm of particle size and 100 g L−1 of pulp density. The kinetic model (I): ((1-α)^-1/3-1)+\\frac13ln(1-α)=k_1t was found to be the most suitable to describe the leaching process of Pt, Pd and Rh in the NaClO contained solution. In this model the interface transfer and diffusion across the leached support layer both affect the rate of leaching reaction. Model (II): (1-(1-α)^1/3)^2=k_2ln(t) fits the kinetic data very well for the dissolution of Pd in the HCl–H2O2 solution, showing that the diffusion across the leached support layer mainly affect the kinetic behaviors and the diffusion coefficient is inversely proportional to leaching time t.The NaClO contained solution and HCl–H2O2 solution leaching of Pt, Pd and Rh are strongly dependent on the leaching temperature. In the case of the NaClO contained solution, the activation energy based on model (I) for Pd, Pt and Rh was 63.5, 59.1 and 77.9 kJ mol−1, respectively. It is probably because of that the diffusion of NaClO contained solution across the leached support layer was very slow due to the micro-porous structure of the catalyst; and a high activation energy was needed in effect. Regarding to the leaching in the HCl–H2O2 solution, the activation energy for Pd was 13.4 kJ mol−1 on the basis of model (II).

The use of the chelating resin Dowex M-4195 in the adsorption of selected heavy metal ions from manganese solutions

The increasing demand for batteries of higher performance characteristics has led to the development of several types of manganese dioxides with optimal battery characteristics. One of these types is produced by a partial leach of a manganese ore, to remove the non-manganese metals to a level acceptable for direct use in batteries. The resulting leach solution must, however, undergo treatment to remove the impurity metals. This paper reports the uptake of copper, nickel, cobalt, lead, iron and manganese from manganese chloride leach solution onto the chelating resin Dowex M-4195 in column experiments. The results demonstrate the ability to remove contaminants to an extent satisfying the quality criteria required for the utilization of the manganese chloride solution for preparing manganese chemicals. Column elution tests demonstrated that a two-stage elution scheme whereby sulfuric acid is first used to elute iron, nickel and cobalt from the resin, then a subsequent ammonium hydroxide elution recovers almost all of the copper is superior to a scheme in which ammonium hydroxide is used before sulfuric acid. However, neither of these elution schemes fully eluted all the metals tested in the study.