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Most Suited Extraction Techniques of Iron and Copper
Bhavy Ostawal

Published: 09 November 2022 | Download
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Abstract

This paper explores and conducts a research review on 2 major metals - iron and copper, and discusses various methods of extraction for each one of them while also exploring considered factors to choose the best suited extraction technique such as- affordability, time taken to complete the process, ease of process, and quantity of metal extracted. This paper discusses the methods and results of various other papers which conduct studies on extraction techniques under the influence of factors such as temperature, pressure, time for extraction, amount of extraction etc. The paper goes into further detailed discussion with regards to the pros and cons of all the mentioned extraction techniques to recommend which of the techniques would be most suitable and practically feasible for each of these metals.

Keywords: iron, copper, extraction, factors

Introduction

Iron

Iron is one of the most commonly used metals. It is a chemical element having the symbol ‘Fe’, given by the International Union of Pure and Applied Chemistry (IUPAC), and the atomic number 26. It belongs to the first transition series, the period 4 and group 8 of the Modern Periodic table. Iron is a good conductor of both heat and electricity. Iron exists in solid state at Standard Temperature and Pressure (temperature-0ºC and pressure-1atm), is the fourth most common element in the earth’s crust and it forms much of the inner and outer core of the earth. Iron is used in production of steel (an alloy), architecture, vehicles, etc. Iron doesn’t exist in its pure form in nature. Rather, it exists in the form of ores (ores are naturally occurring solid materials from which a metal can be extracted). Some of the major iron ores are:

1. Magnetite (Iron (II, III) oxide-Fe3O4, Contains 72.4% Fe)
2. Hematite (Iron (III) oxide-Fe2O3, Contains 69.9% Fe)
3. Goethite (FeO(OH) , Contains 62.9% Fe)
4. Limonite (FeO(OH)·n(H2O), Contains 55% Fe)
5. Siderite (Ferrous Carbonate-FeCO3, Contains 48.2% Fe)
6. Pyrite (FeS2, also called Fool’s Gold)

Copper

Copper is a chemical element having the symbol ‘Cu’, as approved by the IUPAC. It has the atomic number 29 and it belongs to group 11, period 4 of the D-block in the Modern Periodic table. It is a soft, malleable and ductile metal (Ko et al., 2021), having a very high thermal and electrical conductivity. Copper is reddish-brown in color, and is one of the very few metals that can occur in a directly usable metallic form in nature, leading to its very early human use in several regions. Copper, like iron, occurs in solid form at STP. It is used as building material, as a constituent of various useful alloys like brass, bronze, and many more. Being a great conductor of electricity, copper is used in electrical wires and various other electrical equipment (Smyrak et al., 2021).

Some of the major copper ores found in nature are:

1. Chalcopyrite (CuFeS₂, Contains 34.5% copper)
2. Chalcocite, also known as copper glance (Cu₂S, Contains 79.8% copper)
3. Cuprite (Cu₂O, Contains 88.8% Cu)
4. Malachite (CuCO₃.Cu(OH)₂, Contains 55.1% Cu)
5. Covellite (CuS, contains 66.5% Cu)

Materials & Methods

Secondary research was conducted in order to find out best extraction techniques for both iron and copper. Various qualitative and quantitative factors were taken into consideration in order to reach a suitable verdict. Data used in this research was taken from research papers published in peer reviewed journals, and well known and accurate books. Various factors (affordability, time taken to complete the process, ease of process, and quantity of metal extracted) were carefully chosen that are important while comparing different extraction techniques. Reliable data from various researches was taken in consideration that helped choose the best technique based on that particular factor. Similar steps were followed for each of the factors. The extraction method that proved to be the best in most of the chosen factors was decided as the best one.

Discussion & Results

1. Different Methods of Iron extraction

Various methods of iron extraction are in use. Some of them are discussed below.

Acidic Extraction: Acidic Extraction methods are used for obtaining iron from its different ores like Ferrihydrite, lepidocrocite, goethite, hematite, magnetite, siderite, and ankerite. All information in this section is taken from a research paper by Raiswell et al. (1994). These methods are:

1. Buffered dithionite. A buffered solution at a concentration of 50 gl^-1 sodium dithionite in a pH 4.8 buffer is prepared. It consists of 0.35 M acetic acid and 0.2 M sodium citrate. Individual extractions are carried out using 50 mg of mineral or 0.2 g of sediment and 50 ml of extractant for around 2 hours. Replication of this extraction technique indicates a precision of ±3-4%. (Raiswell et al., 1994)
2. Cold HCl method. For 24 hours, a 80 ml 1 M HCl solution was reacted with about 50 mg of mineral or 0.5 g of sediment. Replication of this extraction technique indicates a precision of ±7%. (Raiswell et al., 1994)
3. Boiling HCl method. For 1 minute, approximately 0.05-0.1 g of sample and 5 ml concentrated HCl are brought to boil, and then further boiled again for 1 minute. The reaction is quenched by filling the tube with distilled water and then the sediment and solution washed into a volumetric Average precision of ±5% is seen. (Raiswell et al., 1994).

• • Separation using solvent extraction method and Tri-n-butyl Phosphate (TBP). TBP can be used to extract Fe from chloride media. Fe (III) can be separated from its chloride solution by this technique. FeCl₃ is used as iron source in aqueous solution. TBP and Kerosene are mixed to provide the organic phase. A flask containing equal volumes (20ml) of aqueous, mixture of hydrochloric acid and definite initial concentration of Fe and organic phases is taken. The mixture is mechanically agitated for 30 minutes at 400 rpm. Mixture is then separated using a decanting funnel for 15 min, allowing full separation. The metal content of the aqueous phase is determined by atomic absorption spectroscopy and then the organic phase is estimated by mass balance calculations. (Sadeghi, & Alamdari, 2014)

2. Factors considered when choosing the best iron extraction technique

1. Affordability. Since the cold HCl method requires very few materials, it can be considered the most affordable technique for iron extraction.
2. Easy to carry out. Separation using solvent extraction method and Tri-n-butyl Phosphate (TBP) isn’t as easy as it consists of methods like separating through decanting funnel (Sadeghi, & Alamdari, 2014). Timed extraction data for the dithionite technique (Canfield, 1988) and the cold HCI technique (Leventhal and Taylor, 1990) have shown that the longer extraction times used (dithionite-2 hour, cold HCl-24 hour) are simple to control such that any resulting variations in the amounts of iron extracted are minimal. The boiling HCl method on the other hand has been criticized as it requires careful control of the extracting conditions, especially due to the short 2 min extraction time (Leventhal and Taylor, 1990).
3. Quantity of iron obtained. Referring to Table 1 below, it can be observed that the boiling HCl method is the best technique in regards to this factor, as it can be used to obtain the most amount of iron as this method extracts nearly all of the total iron content present in the ores (like Ferrihydrite, magnetite, ankerite, etc). Referring to the table below, it can be observed that the Dithionite method leads to wastage of iron from some of the ores like magnetite, siderite, and ankerite but is good when extracting from ores like ferrihydrite, lepidocrocite, goethite and hematite. The cold HCl method is the worst in this case as it causes a large wastage of iron when extracting from ores like lepidocrocite, Goethite, magnetite and hematite.  

Table 1: Weight (%) Fe extracted from the above minerals using each extraction, compared to the total iron content. Source: Raiswell et al. (1994)

4. Time taken. The quickest method is the boiling HCl method of extraction (2 min) and the longest one is cold HCl method (24 hours).

3 Different Methods of Copper Extraction

1. Extraction of copper from low grade ores and scraps. Copper is extracted from low grade ores through hydrometallurgy. It is leached out using acid or bacteria . The solution which contains Cu²⁺ cation is treated with H₂ or scrap iron. Reactions involved are-

• Cu²⁺ (aq) + Fe (s) → Cu (s) + Fe²⁺ (aq)
• Cu²⁺ (aq) + H₂ (g) → Cu (s) + 2H⁺ (aq)

(Narlikar et al., 2015)

2. Leaching of Cuprite (Copper oxide) through NH₄OH (Ammonium Hydroxide). Cuprite is a difficult oxide to leach under acidic conditions, so leaching in an ammoniacal medium (basic) can be used (Aracena et al., 2018). The leaching process is performed in a 2 L glass reactor equipped with a variable mechanical stirrer, a heating element, a thermocouple, a porous liquid sample tube and a water-cooled condenser to minimize the solution loss from evaporation (Aracena et al., 2018). Figure 2 (Aracena et al., 2018) below shows the experimental equipment.