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Understand Phytomining and Bioleaching

In this worksheet, students will learn how plants and bacteria are used to extract metals from ores. Students will also evaluate phytomining and bioleaching in comparison with conventional methods for extracting metals.

Worksheet Overview

QUESTION 1 of 10

The main ways of extracting metals from ores are heating with carbon and electrolysis. Both of these methods use large amounts of energy. That means they are only really viable for ores with high concentrations of metal, called high grade ores. Even then, energy use harms the environment. Scientists are developing new ways of extracting metals from lower grade ores using less energy. Phytomining and bioleaching are two of these methods.

Phytomining uses plants to absorb metal compounds from the soil they grow in. All plants have the ability to absorb and concentrate chemicals from the soil via their root systems; that's how they get nutrients they need to grow.

Some plants have evolved the ability to absorb and store metals from the ground in their leaf systems. These plants- called hyperaccumulators- have a survival advantage over normal plants, because they are able to grow in metal-rich soils where other plants cannot survive.

We can exploit hyperaccumulation to extract metals from low grade ores. If we grow the right hyperaccumulator plant on the ore, it will absorb the metal we want to extract from the ground. We can collect the leaves from the plants; these will contain high concentrations of the metal we want. We typically burn the leaves, and use acid to extract the metals from the ash.

Compared with normal mining followed by heating with carbon or electrolysis, phytomining has several advantages;

  • The ore does not need to be mined and removed for processing.
  • Much less waste material is produced.
  • Most of the processing happens at lower temperatures, reducing energy use.
  • Phytomining can work well with lower grade ores, increasing the overall supply of metals.

However, phytomining is a slow process, and produces fairly small amounts of metal, compared with conventional techniques.

Another way of using phytomining is to remove toxic metals from contaminated ground. If we grow hyperaccumulators on contaminated ground, they will remove the toxic substances from the soil, making it safe to use again.

Bioleaching uses bacteria, rather than plants, to remove metals from compounds. Some bacteria can extract energy from the chemical bonds in sulfate compounds, such as copper sulfate. When they do this, they produce a copper-rich solution, called a leachate. We can extract the copper from this with electrolysis or by a displacement reaction with scrap iron;

Cu2+(aq) + Fe(s) → Cu(s) + Fe2+(aq).

Like phytomining, bioleaching is a useful method for extracting metals from low-grade ores. This is particularly important for copper, where high-grade ores are increasingly rare. It also uses less energy than smelting. However, some of the chemicals produced in the process are harmful, and the process is relatively slow and expensive.

What are the two main methods used at the moment to extract metals from ores?

Bioleaching

Electrolysis

Phytomining

Smelting (heating with carbon)

What are the principal benefits of phytomining and bioleaching?

They can extract more metal from an ore.

They use less energy than other methods.

They can work with lower grade ores.

They work faster than other methods.

What does a high grade ore mean?

An ore with no toxins.

An ore with a high concentration of the element being extracted.

An ore that breaks easily.

In phytomining, which part of the plant extracts metals from the soil?

In phytomining, which part of the plant do we collect to extract the metals?

What are the main disadvantages of phytomining, compared with conventional methods of metal extraction?

Phytomining doesn't work on solid rock

Phytomining is slower then smelting or electrolysis.

Phytomining produces smaller amounts of metal than smelting or electrolysis.

Phytomining only extracts copper

What type of metal extraction uses bacteria?

Which of these phrases describes a leachate?

liquid metal

produced by acid

metal-rich solution

produced by bacteria

Complete this paragraph about bioleaching, using these words;

atoms

ions

iron

less

more

liquid metal

produced by acid

metal-rich solution

produced by bacteria

Mark this paragraph about bioleaching; tick each correct sentence.

Bioleaching is a way of extracting metals from low-grade ores using bacteria.

An example of bioleaching is to extract copper from copper sulfate.

There are lots of high-grade copper ores available.

Bioleaching uses small amounts of energy.

Bioleaching produces no harmful byproducts

  • Question 1

What are the two main methods used at the moment to extract metals from ores?

CORRECT ANSWER
Electrolysis
Smelting (heating with carbon)
EDDIE SAYS
The main methods used are still electrolysis and smelting. Bioleaching and phytomining are potentially important for the future, but they are still niche methods for now.
  • Question 2

What are the principal benefits of phytomining and bioleaching?

CORRECT ANSWER
They use less energy than other methods.
They can work with lower grade ores.
EDDIE SAYS
Biological methods use less energy, because they work at normal temperatures. Smelting and electrolysis only work at high temperatures, so need lots of energy. Because the cost of energy is lower, biological methods are viable when working with lower grade ores.
  • Question 3

What does a high grade ore mean?

CORRECT ANSWER
An ore with a high concentration of the element being extracted.
EDDIE SAYS
The grade of an ore is another name for describing the concentration of the element being extracted. It's relevant because biological methods of extracting metals are viable with low grade ores.
  • Question 4

In phytomining, which part of the plant extracts metals from the soil?

CORRECT ANSWER
root
roots
EDDIE SAYS
Plant roots extract elements from the soil anyway- that's how they collect essential nutrients. The different thing about phytomining is that plants extract metals they don't really need to grow.
  • Question 5

In phytomining, which part of the plant do we collect to extract the metals?

CORRECT ANSWER
leaf
leaves
EDDIE SAYS
In phytomining, we take the leaves from the plants, and burn them to extract metal.
  • Question 6

What are the main disadvantages of phytomining, compared with conventional methods of metal extraction?

CORRECT ANSWER
Phytomining is slower then smelting or electrolysis.
Phytomining produces smaller amounts of metal than smelting or electrolysis.
EDDIE SAYS
The advantages and disadvantages of phytomining are linked to its use of plants. The amount and rate of metal extraction are limited to what the plant roots can collect.
  • Question 7

What type of metal extraction uses bacteria?

CORRECT ANSWER
bioleaching
EDDIE SAYS
Bioleaching uses bacteria (so the b's match up). Phytomining uses plants (so the p's match up).
  • Question 8

Which of these phrases describes a leachate?

CORRECT ANSWER
metal-rich solution
produced by bacteria
EDDIE SAYS
The solution produced by the bacteria is called the leachate. It needs further processing to extract the metal.
  • Question 9

Complete this paragraph about bioleaching, using these words;

atoms

ions

iron

less

more

CORRECT ANSWER
EDDIE SAYS
It seems a bit odd to use pieces metal to extract the copper. It makes sense economically, because scrap iron is very cheap and copper is valuable.
  • Question 10

Mark this paragraph about bioleaching; tick each correct sentence.

CORRECT ANSWER
Bioleaching is a way of extracting metals from low-grade ores using bacteria.
An example of bioleaching is to extract copper from copper sulfate.
Bioleaching uses small amounts of energy.
EDDIE SAYS
People are interested in bioleaching copper, because demand is high (we need copper for electric wires), and supplies are running low. Some of the waste products from bioleaching are dangerously acidic, so we have to be careful how we dispose of these.
---- OR ----

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