Reducing Resource Use and the Haber Process

Reduce Reuse Recycle

The three Rs are a hierarchy for managing resources sustainably:

Reduce

Using less of a resource in the first place. This is the most effective strategy because it prevents waste at source.

Examples:

• Using less packaging on products
• Making products that are lighter or use fewer materials
• Reducing energy consumption (insulation, efficient appliances)
• Using digital communication instead of paper

Reuse

Using a product again for the same or a different purpose, without reprocessing.

Examples:

• Refilling water bottles
• Using carrier bags multiple times
• Donating clothes and furniture
• Refurbishing electronics

Recycle

Processing used materials to make new products, reducing the need for raw materials.

Examples:

• Recycling metals — melting scrap metal uses far less energy than extracting from ore (e.g. recycling aluminium uses about 5% of the energy needed to extract it from bauxite)
• Recycling glass — crushed, melted and reformed
• Recycling paper — pulped and reformed
• Recycling plastics — sorted by type, melted and remoulded (only thermosoftening polymers)

Why Recycling Metals Is Important

• Saves energy — extracting metals from ores (smelting, electrolysis) requires huge amounts of energy
• Conserves finite resources — metal ores are running out
• Reduces mining — less environmental damage (habitat destruction, noise, dust, visual pollution)
• Reduces landfill — metals do not decompose
• Reduces CO₂ emissions — less energy used means less fossil fuel burned

Extracting Metals and the Environment

Mining and extracting metals causes significant environmental problems:

• Open-cast mining destroys landscapes and habitats
• Waste rock (spoil heaps) takes up land and can be toxic
• Processing uses large amounts of energy and water
• Smelting releases SO₂ and CO₂
• Electrolysis requires enormous electrical energy

Phytomining and Bioleaching

These are newer methods for extracting metals from low-grade ores (ores with small amounts of metal) or waste tips that cannot be mined economically by traditional methods.

Phytomining:

1. Plants are grown on soil containing the metal compound

2. The plants absorb metal ions through their roots

3. The plants are harvested and burned

4. The metal is extracted from the ash by smelting or electrolysis

Bioleaching:

1. Bacteria are used to produce a leachate solution containing metal compounds

2. The bacteria feed on the metal compounds in the ore, converting them into soluble forms

3. The metal is extracted from the leachate (e.g. by displacement with scrap iron, or electrolysis)

Advantages: can extract metals from low-grade ores and waste; less disruptive than traditional mining

Disadvantages: slow processes; produce toxic waste solutions; limited to certain metals

The Haber Process

The Haber process is the industrial manufacture of ammonia (NH₃) from nitrogen and hydrogen. Ammonia is essential for making fertilisers that feed the world's growing population.

The Reaction

N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

The reaction is reversible and exothermic in the forward direction.

Raw Materials

• Nitrogen — obtained from the air (78% nitrogen) by fractional distillation of liquid air
• Hydrogen — obtained from natural gas (methane) by reacting with steam, or from the electrolysis of water

CH₄ + H₂O → CO + 3H₂ (steam reforming)

Conditions

Condition	Value	Reason
Temperature	450°C	Compromise: lower temp gives higher yield (exothermic forward reaction favoured at low temp) but rate is too slow; higher temp gives faster rate but lower yield
Pressure	200 atmospheres	Higher pressure favours the forward reaction (4 moles of gas → 2 moles of gas) giving a higher yield; very high pressure is dangerous and expensive
Catalyst	Iron	Speeds up the rate of reaching equilibrium; does not change the yield

The Compromise

• The temperature of 450°C is a compromise between rate and yield
• A low temperature gives a high yield but the reaction is too slow to be economical
• A high temperature gives a fast rate but the yield is low
• 450°C gives a reasonable rate with an acceptable yield (~15%)

Recycling Unreacted Gases

Because the yield is only about 15%, there is a lot of unreacted N₂ and H₂. These are recycled — separated from the ammonia (which is cooled and liquefied) and fed back into the reactor. This maximises the overall conversion.

Uses of Ammonia

• Fertilisers — ammonia is converted to ammonium nitrate (NH₄NO₃), ammonium sulfate, or ammonium phosphate
• Nitric acid (HNO₃) — made by oxidising ammonia (used in fertilisers, explosives, dyes)
• Cleaning products — household ammonia solutions
• Nylon and other polymers

NPK Fertilisers

Plants need three essential elements for growth:

Element	Symbol	Source (fertiliser compound)
Nitrogen	N	Ammonium nitrate (NH₄NO₃), urea
Phosphorus	P	Calcium phosphate, superphosphate
Potassium	K	Potassium chloride (KCl)

NPK fertilisers are formulated to provide all three nutrients. They can be made by:

• Neutralising acids with alkalis or ammonia
• Mixing the appropriate salts in the correct proportions

Exam Tips

• Know the order: reduce > reuse > recycle (reducing is most effective)
• Be able to explain why recycling metals saves energy compared to extraction from ores
• For the Haber process: know the equation, conditions and the compromise between rate and yield
• Remember that the iron catalyst speeds up equilibrium but does not change the yield
• Unreacted gases are recycled to improve overall efficiency
• Phytomining and bioleaching are for low-grade ores — know the basic method for each