Is There Ni in My Liquor? A Hands-On Laboratory Exercise for

Laboratory Experiment pubs.acs.org/jchemeduc

Is There Ni in My Liquor? A Hands-On Laboratory Exercise for Relating Chemistry to Extractive Metallurgy Damian W. Laird* and David J. Henry Chemical and Analytical Sciences, School of Veterinary and Life Sciences, Murdoch University, Murdoch, Western Australia 6150, Australia S Supporting Information *

ABSTRACT: A simple, quick, and safe laboratory exercise is detailed that provides a link between chemistry, extractive metallurgy, and hydrometallurgy. Students are provided with a scenario in which they need to “research” a procedure to selectively recover nickel from simple “ore liquors”. In this context, the experiment focuses on the selective precipitation of metal ions from solution using simple chelating agents. Students work in teams to complete separate parts of the experiment, testing a possible procedure for an industry client. The teams then come together as a group to interpret and discuss the results before deciding what to report to the client. The experiment was developed to be completed in a single 40 min session and has been successfully conducted with over 200 middle- to upper-level high school students. KEYWORDS: High School/Introductory Chemistry, Interdisciplinary/Multidisciplinary, Public Understanding/Outreach, Hands-On Learning/Manipulatives, Inquiry-Based/Discovery Learning, Applications of Chemistry, Coordination Compounds, Metals

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three years of high school (15−18 year olds). All of the students were currently studying general science subjects at school but not necessarily chemistry-intensive subjects. The idea behind the program is not necessarily to teach science but rather highlight how science, some of which students have already encountered, can be applied in a practical and relevant way in extractive metallurgy and associated areas. In addition to traditional extractive metallurgy pursuits in hydro- and pyro− metallurgy (such as froth flotation and smelting), we felt it was important to show students that chemical knowledge is important to current practice in this field and for future development. It was also necessary to tie in any chemistryintensive activities to the froth floatation and pyro−metallurgy activities that students would participate in during their visit to the campus. The aim was to make the experience one that challenged participants rather than simply repeat what students might otherwise be able to do in their current classroom or curriculum. This can be achieved by expanding on the basic science and chemistry concepts that students are already aware of or making use of advanced instrumentation not generally available to high schools. Two focused chemistry-based exercises were designed: one highlighting analysis using instrumentation not available to high schools and the other looking at selective removal of metals from mixtures. This paper describes the latter. Apart from the “edutainment” and awareness-building value of the exercise, we also wanted to reinforce general scientific and laboratory procedures. Therefore, the laboratory was designed to include a safety introduction, teamwork, replication of experimental data and observations, and safe laboratory working practices and to be accessible to students with a range of abilities or exposure to laboratory work (from general

he mining industry is a constant presence in Western Australia. Despite the ongoing success and profitability of this industry, the harsh and remote conditions of the mines mean that many companies experience a shortage of skilled workers.1−4 Although the majority of positions available are for skilled tradespeople, there is a strong demand for workers in science-based areas such as geology, mineralogy, process engineering, and metallurgy. Unfortunately, the mining industries, associated processing industries, and universities have noted a decline in the number of students enrolling in the tertiary-level science and engineering-based courses that underpin these industries.5,6 The prevailing opinion for this among recruiters, academics, and industry sources is that high school students are not receiving exposure to the opportunities that may be available to them. The general consensus is that a way needs to be found to enlighten students about the possibilities open to them in mining and the associated areas and to “enthuse” their interest in relevant tertiary studies. To this end, the disciplines of Extractive Metallurgy and Chemical and Analytical Sciences at Murdoch University and Rio Tinto Australia entered into an agreement to develop a one-day outreach program for high school students to be delivered either on the university campus or at non-metropolitan school sites. Students who attended on-campus sessions rotated through a series of four or five 40 min long exercises developed to show how science can be applied in a practical and relevant way. One of the exercises is described in detail here and can easily be carried out in a high school lab.

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THE OUTREACH PROGRAM

The “Extracting Talent for Metallurgy” program was run for the first time in late June 2012 with a mix of students in the final © 2013 American Chemical Society and Division of Chemical Education, Inc.

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reinforce the point that students needed to test whether (a) the two chelators reacted with any or all of the selected metal ions, (b) either of the chelators exhibited selectivity for nickel, (c) any of the other metal ions interfered with selectivity for nickel, and (d) a strategy could be devised to minimize interferences and maximize selectivity.

science up to students undertaking capstone secondary school chemistry). This all needed to be achieved in a single 40 min session.

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THE EXERCISE

Background

Execution

Selective removal of metal ions from a “pregnant” metallurgical liquor can be achieved in a number of ways,7 including manipulation of pH conditions, electrolytic deposition, and ion exchange. We chose to concentrate on chelators as a means of selective precipitation of a metal ion and specifically used simple small chelators: acetylacetone (acac; pentane-2,4-dione) and dimethylglyoxime (DMG; 2,3-butanedione dioxime). Dimethylglyoxime is known to be a selective precipitating agent for nickel,8 whereas acac forms complexes with a wide range of metal ions.9 The use, and performance comparison of, multiple chelating agents for qualitative analysis in a laboratory is unusual. Qualitative analysis approaches are usually restricted to procedures that involve removal of some metals as insoluble sulfides prior to use of a chelating agent to differentiate between two remaining candidates.10−12 Traditional complexation laboratories are often focused on synthesis and spectral characterization of pure complexes or the physical chemistry aspects of complex formation.13−16

To achieve the goals of the testing in the time provided the class was broken into 3 teams: · Team acac testing each of 5 metal ions with acac. · Team DMG testing each of 5 metal ions with DMG. · Team Mix testing solutions of two metal ions. For Teams acac and DMG, it was made clear that we were really interested in which metals formed a precipitate and what color it was. Students should record if the solution changed color, but the precipitate would be the most important observation. Each team member tested three of the five metal ion solutions and then they compared results to make sure all matched. If there was an anomalous result then that metal was tested again. Once all team members had agreed on the results they recorded them in a table on a whiteboard at the front of the lab. For Team Mix, there was an initial discussion about how they could prove that any observed precipitate contained only one of the two metal ions in their mixtures. Students began by testing the mixture with DMG. If they observed a precipitate, they then separated the remaining solution from the precipitate using a microcentrifuge (small scale vacuum filtering would also work), and retested the solution with acac to show if the other metal ion was still present. This exercise took longer than the individual tests performed by the other teams and, therefore, each student tested only two mixtures, making sure that the group as a whole had tested all four of the mixtures available. Again students were asked to compare their results, retest if necessary, and put agreed results up on the whiteboard at the front of the lab. Once all results had been collated, the three teams came together to analyze the overall message from the data. They initially focused on the single metal ion results to identify whether one chelator was more selective for nickel. The group then identified whether those results translated to the mixtures. Finally, there was discussion about what to report to the client, for example, · Does the concept work? · Was one of the chelators more selective than the other? · Were there any possible interferences?

Materials

Due to the time constraints and unknown extent of laboratory experience of the students, all solutions were preprepared and provided in labeled bottles equipped with eye-dropper lids. Students only had to use the dropper to transfer a solution to a measuring cylinder or test tube. Concentrations for the metal ion solutions were in the range 0.2−0.3 M. Metal ion mixtures were 1:1 mixtures of the single metal ion solutions. The chelator solutions were 2:5 acetylacetone:methanol and 1% dimethylglyoxamate in ethanol (see the Instructor Notes in the Supporting Information for details). Scenario

A scenario was devised stating that the group had been contracted by a minerals processing company to provide information on the possibility of selectively removing Ni from a hydrometallurgical liquor potentially also containing Fe, Co, Cu, and Mn (see the Supporting Information for student handouts and worksheets). It was pointed out that though froth flotation can selectively remove minerals from a mixture, it cannot separate out the metal ions from those minerals. To achieve this next step requires an understanding of solution and coordination chemistry. Therefore, the focus of the laboratory presented here is to introduce students to some simple coordination chemistry and to demonstrate its value in separating out metal ions from dissolved minerals. In this context, a brief introduction was provided on the concept of chelation, including examples of common chelate complexes, such as heme and chlorophyll, and an understanding that some chelators can be selective for metal ions of specific charge or size. Students were introduced to the two chelating agents that they would be trialing, and there was a brief discussion on how the organic compound was binding to the metal ion through the lone pairs of electrons on the O or N. This showed that there was a distinct difference in the two chelating agents and that this might lead to specificity. Then there was a facilitated discussion about how to best achieve results in the time available. In particular we wanted to

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HAZARDS Students were required to wear personal protective equipment (laboratory coat, lab glasses, and covered shoes) at all times in the laboratory and were given the option of suitable gloves. None of the complexes were considered to be hazardous, particularly because they were mostly contained within solution or an aqueous mixture. The students were given detailed instruction and assistance when using the centrifuge to prevent breakage of glass microcentrifuge tubes. The ethanolic or methanolic chelator solutions are flammable, and no naked flames should be in the laboratory. Standard precautions should be taken by staff preparing the solutions. The transition metal salts and solid DMG are considered toxic if inhaled or ingested. All of the transition metals utilized can be considered toxic to 1672

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the selective complexation of metal ions, has been delivered to over 200 students and found to be suitable for use with high school students with the ages of 15 years and older. The teamwork and investigative aspects of the exercise were valuable for stimulating discussion of not only this experiment but also the general concepts and uses of metal ion complexation.

aquatic life, and waste was collected for disposal by an appropriate commercial operator.

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RESULTS The results produced by Team acac and Team DMG were consistent for all 24 sessions (Table 1). Results for Team Mix

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Table 1. Typical Results from Reaction of Metal Ion Solutions with Chelators

S Supporting Information *

Chelator Metal(s)a Ni Cu Co Fe Mn Ni + Ni + Ni + Fe +

Cu Fe Mn Co

acac precipitate

DMG precipitate

Pale green Blue-gray Pale pink Orange-red Black-brown Blue-purple Orange-red Brown Dark red

Pink-red No No No Black-brown Pink-red Pink-red Black-brown No

ASSOCIATED CONTENT

Student worksheets, instructor notes. This material is available via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*D. W. Laird. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This experiment was developed as part of the “Extracting Talent for Metallurgy” program for high school students, which is generously funded by Rio Tinto Australia. The authors thank Andrew Foreman, Tina Oteri, Saijel Jani, Aaron Brown, Ben Anandappa, and Darryl Chung for their assistance in the development and initial testing of this experiment.

DMG was first added to the mixtures; if a precipitate resulted, the precipitate was removed and acac was added to the supernatant.

a

were more variable and the most consistent results were produced by those students who had previously had a greater exposure to laboratory work.

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DISCUSSION Dividing the students into teams worked well. It was found that one demonstrator could supervise Teams acac and DMG, and a second demonstrator could then assist Team Mix to complete the more challenging part of the experiment. However, the success or failure to differentiate between the metals was less important than having students predict what they thought would happen in the mixtures based on the results of the simpler single metal ion tests. In fact, we deliberately included a mixture containing Mn and Ni, both of which are precipitated using DMG to show that although the simple concept worked, there may need to be some caveats to using it on more complex mixtures. In fact, we found that the failure of the prediction was the most useful circumstance for stimulating discussion on the concepts of complexation, the need to fully characterize products from reactions, and the possibility that an experiment may not work as predicted. These discussions then often led to further interest in how the concept of complexation could be used in other areas such as drug development, environmental remediation, chemical catalysis, and so forth. Our goal was to provide a hands-on exercise showing links between chemistry and extractive metallurgy and highlighting the teamwork required in a professional setting, not to specifically teach the chemistry of the exercise. However, we do believe that this experiment could be the centerpiece or introduction to a deeper exploration into coordination chemistry. Concepts such as complexation reactions, solubility, product characterization, data analysis, and reporting to clients could be expanded upon quite easily.

REFERENCES

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CONCLUSION A quick and simple hands-on laboratory introducing and highlighting the connection between chemistry and hydrometallurgy has been developed. The experiment, based around 1673

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(14) Thompson, D. W. Inorganic Derivatives of Acetylacetone. J. Chem. Educ. 1971, 48, 79−80. (15) Ribeiro, M. G. T. C.; Machado, A. A. S. C. MetalAcetylacetonate Synthesis Experiments: Which Is Greener? J. Chem. Educ. 2011, 88, 947−953. (16) Long, S. R.; Browning, S. R.; Lagowski, J. J. The Electrochemical Synthesis of Transition-Metal Acetylacetonates. J. Chem. Educ. 2008, 85, 1429−1431.

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