✅ C619 Biological metal extraction

Question 1

What is acid mine drainage - and hows this related to bioleaching
94)

Answer 1

• mines often flood when they are abandoned
• metal sulfide oxidise underwater, producing sulfuric acid, which reacts with other metal ores
• soluble metal compounds form, and these leave with the water as it drains from the mine
• these reactions happen naturally, but certain bacteria make them go faster - this is the basis of bioleaching

Question 2

How bioleaching works

• and link it to a human body process
• how its a biological metal extraction

(4)

Answer 2

• in respiration, glucose is oxidised and your cells use the energy transferred
• in a similar way, in bioleaching, bacteria oxidise iron(II) and sulfide ions and use the energy transferred
• in this process, sulfuric acid forms in the presence of water and oxygen
• this sulfuric acid breaks down copper sulfide ores and other minerals, releasing copper(II) ions and other metal ions

Question 3

Bioleaching advantages

4

Answer 3

• cheaper than traditional mining and processing
• allows metals to be extracted from ores that contain too little metal for traditional methods to be profitable (called low-grade ores)
• the bacteria occur naturally and do not need any special treatment
• bioleaching does not release harmful sulfur dioxide into the atmosphere (wierd)

Question 4

Bioleaching disadvantages

3

Answer 4

• bioleaching does not release harmful sulfur dioxide into the atmosphere (gases) , BUT IT IS SLOW

toxic substances are sometimes produced:
- care must be taken to avoid these and sulfuric acid, escaping into water supplies and the soil

Question 5

HOW does phytoextraction works

4 steps

Answer 5

• a crop is planted in soil containing a low-grade ore or mine waste
• a ‘complexing agent’ may be added so the plants can absorb the metal ions more easily
• the plants are harvested, and then burnt to produce ash with a high concentration of the metal
• the metal can then be extracted, just as if the ash was a high-grade ore

Question 6

WHY does phytoextraction work\

2 steps

Answer 6

• plants absorb dissolved ions through their roots
• some plants are particularly good at absorbing certain metal ions, which then accumulate in their roots, shoots, and leaves

Question 7

How does the ash become metal

Answer 7

Plant material burnt —> small volume of plant ash (bio-ore) containing high concentration of target metal —> bio-ore smelted to yield metal

Question 8

Why would phytoextaction be used?

Answer 8

• crop grows on soil containing metal concentration too low for conventional exploitation

(Copper/nickel/thallium/gold)

Question 9

Complexing agents may be added to

Answer 9

Enhance metal uptake of crop

Question 10

Phytoextraction adv

3

Answer 10

• cheaper than traditional mining and processing
• produces less waste and involves small energy transfers
• closer to being a carbon-neutral activity than can contribute to sustainable development — burning plants release carbon dioxide, but they absorb carbon dioxide for photosynthesis as they grow

Question 11

Phytoextraction disadv

2

Answer 11

• slow

- crops may need replanting and harvesting for several years before the available metal is removed from the soil

Question 12

Phytoextraction

Plants absorb __ ions through their roots. Phytoextraction makes use of this:

1- plants are grown on a __ grade ore
2- the plants absorb metal ions through their __ and concentrate these ions in their __
3- the plants are __ and __
4- the ash left behind contains a higher __ of the metal than the original ore
5- the ash is __ to obtain the metal

Answer 12

Phytoextraction

Plants absorb mineral ions through their roots. Phytoextraction makes use of this:

plants are grown on a low grade ore
the plants absorb metal ions through their roots and concentrate these ions in their cells
the plants are harvested and burnt
the ash left behind contains a higher concentration of the metal than the original ore
the ash is processed to obtain the metal

Question 13

Phytoextraction is __, but it:

• reduces the need to obtain new ore by __
• conserves limited supplies of __ grade ores

Answer 13

Phytoextraction is slow, but it:

• reduces the need to obtain new ore by mining
• conserves limited supplies of high grade ores

Question 14

Suggest reasons why phytoextraction reduces damage to the environment.
- basically why traditional mining is bad

Answer 14

Mining for metal ores involves quarries, which are large holes in the ground. These create noise, dust and traffic. They also destroy natural habitats. Phytoextraction reduces the need for mining, so reduces this damage.

Question 15

Bacterial extraction

Certain bacteria can break down low __ ores to produce an __ solution containing copper ions. The solution is called a __ and the process is called bioleaching. Bioleaching does not need high __, but it produces __ substances, including __ acid, which damage the environment.

Answer 15

Bacterial extraction

Certain bacteria can break down low grade ores to produce an acidic solution containing copper ions. The solution is called a leachate and the process is called bioleaching. Bioleaching does not need high temperatures, but it produces toxic substances, including sulfuric acid, which damage the environment.

Question 16

Using scrap iron

Iron is more reactive than __. It can displace copper from the __. For example:

iron + copper sulfate → iron(II) sulfate + copper

Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)

Since iron is cheaper than copper, the use of scrap iron is a __-effective way to produce copper from the __.

Answer 16

Using scrap iron

Iron is more reactive than copper. It can displace copper from the leachate. For example:

iron + copper sulfate → iron(II) sulfate + copper

Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)

Since iron is cheaper than copper, the use of scrap iron is a cost-effective way to produce copper from the leachate.

Question 17

Tell us about bioleaching

Answer 17

Bioleaching is a technique that makes use of bacteria to extract metals from metal ores
Some strains of bacteria are capable of breaking down ores to form acidic solutions containing metals ions such as copper(II)
The solution is called a leachate which contains significant quantities of metal ions
The ions can then be reduced to the solid metal form and extracted by displacement reactions or electrolysis
This method is often used to extract metals from sulfides e.g. CuS or Fe2S
Although bioleaching does not require high temperatures, it does produce toxic substances which need to be treated so they don’t contaminate the environment
Bioleaching is not only used for the primary extraction of metals, but it is also used in mining waste clean up operations