Electrochemistry and light metals
Use electricity to do chemistry that heat cannot.
Everything for this step
- Field guide
- Electricity → 8 sections Chemistry → 9 sections
- Builds
- None yet.
- Reference sheets
- 7 sheets in Electricity
- Track
- Metals, level 4 of 4
Why this matters
Some elements are bound too tightly to be freed by carbon at any temperature. Electricity breaks those bonds directly — which is the only route to aluminium, chlorine, caustic soda and pure metals. It is also why aluminium was once more valuable than gold and then became cheap enough for cooking foil.
The shape of it
- Start with brine electrolysis — the chlor-alkali process. Salt water plus electricity gives chlorine, hydrogen and sodium hydroxide, all three of which you want. Chlorine alone transforms water treatment.
- Then electroplating, which is easy and high value: copper, zinc, tin and nickel coatings that stop steel rusting. Corrosion protection extends the life of everything you have built.
- Then refining. Electrolytic copper refining gives the high-purity copper that good conductors require. Impure copper has significantly worse conductivity, so this loop feeds itself.
- Then aluminium by the Hall–Héroult process: alumina dissolved in molten cryolite, electrolysed with carbon anodes. It is enormously power-hungry — aluminium smelting is essentially a way of turning electricity into metal — but it gives a light, corrosion-resistant structural metal you cannot get any other way.
- Site power-hungry electrochemistry at the power source, typically hydroelectric. It is far cheaper to move the ore than the electricity.
- Handle chlorine with extreme care. It is heavy, it pools in low ground, and it destroys lung tissue. Ventilate, monitor and never work alone.
- Then build storage. Lead-acid cells are makeable at this tier and turn intermittent generation into a reliable supply — which is what lets a small settlement run on water or wind without a continuous prime mover.
Doing it, step by step
The summary above says what has to happen. This says how, with the numbers that decide whether it works.
1 · Budget the power before you start
Electrochemistry eats electricity, and underestimating the demand starves the rest of the settlement. Aluminium takes roughly 13–15 kWh per kilogram; chlorine and caustic soda a few kWh per kilogram; electroplating far less.
Write a power budget: the settlement's existing load, the new process's load, and the generation available in the dry or calm season. Site power-hungry processes at the power source — typically hydroelectric — because it is far cheaper to move ore than electricity.
2 · Electroplate steel to stop it rusting
Easy and high value. Clean the part — degrease in hot alkali, rinse, dip in dilute acid to remove rust and scale, rinse again. Any film left on the surface makes the plating peel.
For copper: a copper sulphate bath acidified with sulphuric acid, the part as cathode, a copper plate as anode, low current. Too much current gives rough, burnt, powdery plating; start low and increase until the coating is bright and even. Zinc protects steel best — the zinc corrodes first, protecting the steel even where scratched. Hot-dip galvanising — dipping cleaned steel in molten zinc at about 450 °C — gives a thicker coat without electricity.
3 · Refine copper for conductors
Impure copper conducts significantly worse, so generator windings and transmission lines made from it waste power. Electrolytic refining: impure copper cast as the anode, thin pure copper sheet as the cathode, in acidified copper sulphate, at low current.
Copper dissolves from the anode and deposits pure on the cathode; impurities fall to the bottom as anode slime — which carries recoverable silver and gold. Measure the product by resistance of a drawn wire against a reference.
4 · Electrolyse brine, and handle chlorine as the poison it is
Salt water plus electricity gives chlorine, hydrogen and sodium hydroxide, all three useful — chlorine transforms water treatment. Use a membrane or a non-asbestos diaphragm to keep the products apart. Do not use mercury cells — they contaminate persistently and are not worth it — and do not use asbestos.
Chlorine is about 2.5 times heavier than air, pools in low ground and basements, and destroys lung tissue. You smell it at a fraction of a part per million; at around 10 ppm it is immediately dangerous to life. Ventilate at floor level, store cylinders upright and outdoors in shade, and never work alone.
5 · Handle the hydrogen as a fire and explosion hazard
The hydrogen from brine electrolysis burns in air across a very wide mixture range — about 4% to 75% — with an almost invisible flame in daylight, and it leaks through gaps other gases cannot.
Collect it in sealed piping to a use — burning it for heat, or for synthetic nitrogen — or vent it high, outdoors, away from any ignition source. No flames, sparks or unrated electrical switches in the cell room. Detect leaks with soapy water on joints, never a flame.
6 · Make aluminium only where power is cheap and abundant
The Hall–Héroult process: alumina dissolved in molten cryolite at about 950–980 °C, electrolysed with carbon anodes, which burn away and are replaced. It is aluminium smelting turning electricity into metal, and it gives a light, corrosion-resistant structural metal available by no other route.
Be honest about scale: a pot line needs continuous, very large current, a steady alumina supply refined from bauxite, and cryolite. The fumes carry fluorides that damage lungs and bones, and harm crops and livestock downwind — capture them. Scavenged aluminium is far cheaper than smelted — recycling needs about a twentieth of the energy.
7 · Build lead-acid storage
Storage turns intermittent generation into a reliable supply, which lets a small settlement run on water or wind without a continuous prime mover. Lead plates in sulphuric acid, about 2 V per cell — six cells for a 12 V battery.
Charge state is read from the acid: electrolyte weighing about 1.28 kg per litre is fully charged, falling toward 1.1 when flat. Never leave them flat — the plates sulphate and are ruined. Charging gives off hydrogen: ventilate, no sparks. Lead is a poison — handle plates with gloves and wash, and recycle every battery's lead.