Extraction and Refining of Metals & Reactivity Series

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Questions and Answers

What is a reactivity series?

A reactivity series is an empirical, calculated, and structurally analytical progression of a series of metals, arranged by their "reactivity" from highest to lowest.

What is a metal ore?

A metal ore is a rock containing a metal, or a metal compound, in a high enough concentration to make it economic to extract the metal.

What are the major steps in the extraction of metal?

Mining, processing, and refining

Ore concentration, reduction to crude metal, and refining to obtain pure metal (correct)

Smelting, casting, and machining

Exploration, extraction, and purification

What are the three methods used to extract metals from their ores?

The three methods are electrolysis, reaction with carbon or carbon monoxide, and various chemical reactions. Signup and view all the answers

Why is electrolysis used to extract highly reactive metals?

Highly reactive metals are found in very stable compounds, so carbon cannot displace them from their ores. Electrolysis is needed to extract these metals. Signup and view all the answers

What is electrolysis?

Electrolysis is a technique that uses a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. It is commercially important as a stage in the separation of elements from naturally occurring sources such as ores using an electrolytic cell. Signup and view all the answers

What are the main components required for electrolysis?

The main components required for electrolysis are an electrolyte, a direct current (DC) electrical supply, and two electrodes Signup and view all the answers

Why is molten cryolite used in the extraction of aluminum?

Molten cryolite is used to lower the melting point of aluminum oxide from about 2000°C to about 900°C, making the extraction process more efficient. Signup and view all the answers

What happens at the cathode during the electrolysis of aluminum oxide?

At the cathode, aluminum ions (Al³⁺) gain 3 electrons from the cathode to form molten aluminum, which is tapped off. Signup and view all the answers

How is iron extracted from iron ore?

Iron is extracted from iron ore using a blast furnace. Signup and view all the answers

What are the raw materials used to extract iron from iron ore?

The raw materials used are iron ore (e.g., haematite ore, which contains iron(III) oxide, Fe₂O₃), coke (carbon, C), hot air (for the O₂ in it), and limestone (calcium carbonate, CaCO₃). Signup and view all the answers

What is the first step in the extraction of iron from iron ore?

The first step is the production of carbon dioxide. Signup and view all the answers

What is the second step in the extraction of iron from iron ore?

The second step is the production of carbon monoxide. Signup and view all the answers

What is the effect of carbon in iron and steels?

The effect of carbon in iron and steels is that it is mainly responsible for the immense range of strengths and other useful properties that can be developed in iron and steels. Signup and view all the answers

What are the main iron ores?

The main iron ores are haematite (Fe₂O₃), magnetite (Fe₃O₄), limonite (2Fe₂O₃.H₂O), hydrates haematite, and siderite (FeCO₃). Signup and view all the answers

What is the melting point of iron?

The melting point of iron is about 1535°C. Signup and view all the answers

Why is cast iron brittle?

Cast iron is brittle because of the presence of carbon and other impurities that form brittle iron-carbide in it. Signup and view all the answers

How are low reactivity metals extracted from their ores?

Low reactivity metals are extracted from their ores by roasting ore by heating alone. They are found as the elements themselves, meaning you don't need to separate them chemically. Signup and view all the answers

Why is gold often found as a native metal?

Gold is very unreactive and is found as a native metal because it does not easily form compounds. Signup and view all the answers

What is the first step in the extraction of gold from its ore?

The first step is to break down large chunks of rock into smaller pieces. Signup and view all the answers

What is leaching?

Leaching is a process that dissolves gold out of the ore using a chemical solvent. Signup and view all the answers

How is gold separated from the ore?

Gold is separated from the ore by a series of leaching tanks, where gold is dissolved out of the ore using a chemical solvent. The gold-bearing solution is then passed through a series of screens to remove carbon grains. The gold is then recovered from the leaching chemicals by electrowinning, in which gold-bearing solution is poured into a cell with positive and negative terminals. A strong electric current is applied to the solution, causing gold to collect on the negative terminals. The gold is then smelted by melting the negative terminals in a furnace at about 2,100 degrees F (1,149 degrees C). A chemical mixture known as flux is added to the molten material, causing the gold to separate from the metal used to make the terminals. The flux and gold are then poured off separately, and the gold is molded into solid bars called doré bars. Signup and view all the answers

Why is refining the last step in metallurgy?

Refining is the last step in metallurgy because it is the process of purifying the metal, achieving the desired quality and purity. Signup and view all the answers

What are the four main processes used for refining metals?

The four main processes are liquation, distillation, oxidation, and electrolytic refining. Signup and view all the answers

What is liquation?

Liquation is a refining process that involves melting a metal and allowing it to flow down a sloping surface, leaving behind impurities that have a higher melting point. Signup and view all the answers

What is distillation?

Distillation is a refining process that involves heating a volatile metal to its boiling point, and then condensing the vapor to obtain a pure metal. Signup and view all the answers

What is electrolytic refining?

Electrolytic refining is a refining process that involves using electrolysis to separate pure metal from impurities. Signup and view all the answers

How is electrolytic refining used to purify copper?

In electrolytic refining of copper, a block of impure copper is made the anode and a thin sheet of pure copper is made the cathode. The impure copper is dissolved into the electrolyte and deposited as pure copper onto the cathode. Impurities remain behind as anode mud. Signup and view all the answers

Study Notes

Extraction and Refining of Metals

The Earth's crust contains metals and metal compounds like gold, iron oxide, and aluminum oxide
Metals are often mixed with other substances in the Earth
To obtain useful metals, they must be extracted from the mixed substances
A metal ore is a rock containing a metal or metal compound in a high enough concentration to make extracting the metal economical
Major steps in metal extraction:
- Ore concentration: purifying and concentrating the ore, removing unwanted rocks
- Reduction to crude metal: reducing metal oxides to pure metals, creating a mixture
- Refining: purifying the metal and removing impurities to obtain a pure metal

Reactivity Series

A reactivity series is an empirical, calculated, and structurally analytical progression that arranges metals by their reactivity, from highest to lowest
Reactivities from highest to lowest are listed in the image
Reactivity series is used to summarize information about reactions of metals with acids, water, and double displacement reactions
It displays the extraction method of metals from their ores

Electrolysis

Highly reactive metals are extracted using electrolysis from their ores due to the formation of very stable compounds that make reduction by carbon unfeasible
Electrolysis uses a direct electric current to drive a non-spontaneous chemical reaction
Electrolysis is commercially important for separating elements in ores using an electrolytic cell. Voltage needed for electrolysis is called the decomposition potential
Electrolysis passes a direct electric current through a molten or dissolved ion-containing substance or electrolyte, creating chemical reactions at the electrodes, and separating materials
Main components for electrolysis are:
- Electrolyte: an ion-conducting substance, usually a polymer that contains free ions to carry current through the electrolyte (solid salts cannot conduct current unless molten)
- DC electrical supply: provides energy to create or discharge ions in the electrolyte.
The external circuit's current is carried by electrons

Electrolysis: Extraction of Aluminum from Bauxite

Raw materials
- Bauxite (Al₂O₃∙2H₂O): an ore containing hydrated aluminum oxide
- Cryolite (Na₃AlF₆): a sodium aluminum fluoride, used to lower the melting point of bauxite
- Carbon electrodes
Melting Point: about 2000°C
Cryolite is added to lower the melting point to about 900°C
In electrolysis, the aluminum ions are attracted to the negative cathode and oxygen ions to the positive anode.
Aluminum ions gain electrons, forming molten aluminum at the cathode. Oxygen loses electrons to form oxygen gas at the anode, reacting with the carbon anode and creating Carbon monooxide/carbon dioxide requiring regular replacement

Reduction with Carbon (Blast Furnace Method): Extraction of Iron

Raw Materials
- Iron ore (e.g., haematite, Fe₂O₃)
- Coke (C)
- Limestone (CaCO₃)
Iron is extracted from iron ore in a blast furnace
Reactions during iron extraction:
- Coke (carbon) reacts with oxygen from hot air to produce carbon dioxide
- Limestone decomposes to calcium oxide and carbon dioxide
- Carbon monoxide reacts with iron oxide ore to remove oxygen and free the iron
Impurities (silica) react with limestone to form a molten slag
The molten iron, denser than the slag, sinks to the bottom of the furnace, creating pig iron

Reduction with Carbon: Extraction of Iron - Stages

Stage 1: Production of carbon dioxide. Coke burns in air to form CO2. The limestone also decomposes into quicklime (CaO) and CO2
Stage 2: Production of carbon monoxide. The carbon dioxide formed from the limestone reacts with more coke to form carbon monoxide
Stage 3: Reduction of haematite. The carbon monoxide removes the oxygen from iron oxide (in the ore), releasing pure iron that's molten due to the high temperature. This iron flows down to the base of the furnace as pig iron.
Stage 4: Removal of impurities. Silica from the ore reacts with calcium oxide to form calcium silicate (slag), which floats on the molten iron. The impurities are removed from the iron.

Refining of Metals

Most metals obtained via reduction are impure. They need further refining
Refining is based on the difference in properties between metals and their impurities
Common refining methods:
- Liquation: melting the metal; low-melting metals like tin, lead are purified by liquation, where the pure metal melts and flows, leaving impurities behind
- Distillation: used for volatile metals; heated to generate vapors to be condensed and purified; impurities are left behind
- Oxidation: removing impurities by oxidation of impurities to form gaseous oxides, which are removed
- Electrolytic refining: used for purifying impure metals like copper; involves making the impure metal the anode and pure metal as the cathode; current passing through electrolytic cell dissolves anode leaving behind purer metal at the cathode

Extraction of Low Reactive Metals

Metals found at the bottom of the reactivity series are often found in their native forms. They can be extracted from their ores by heating or roasting. Gold, for example, is often found as a native metal and does not usually require chemical separation. Other chemical reactions may be needed to remove contaminants.

Extraction of Gold

Gold extraction involves breaking down large rock chunks into smaller pieces, grinding to a slurry or powder, thickening the slurry with water to form pulp, and processing it through leaching tanks.
Cyanide leaching dissolves the gold, a chemical solvent. It's important to combine it with oxygen in the carbon-in-pulp process to allow dissolution.
Small carbon grains are introduced to the leaching solution; gold adheres to the carbon. A filter mechanically separates the gold from the carbon.
A hot caustic solution separates the gold from the carbon in a stripping vessel.
Additional filtration processes are used to remove the remaining carbon and other materials using screens.
Electrowinning is used to separate the gold using a specialized cell. A current passes through the solution, which causes the gold to collect on the negative terminals.
Smelting, involves melting the negative terminals in a high temperature furnace which causes the gold to become nearly pure. A flux is added to separate the gold from the terminals.
Molds transform the molten gold into gold bars called doré bars during final steps of the process.

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Description

This quiz covers the essential processes involved in the extraction and refining of metals, including the concentration of ores and the reduction to pure metal. Additionally, it introduces the reactivity series, which ranks metals based on their reactivity levels. Test your understanding of these fundamental concepts in metallurgy.