Material Insights · Understanding the Material World

Caustic soda and Salt

Caustic soda is made by passing electricity through salt brine, so each tonne needs roughly one and a half tonnes of salt, but salt is cheap and power is not. The link that matters is physical and geographic: salt quality for membrane cells and access to coastal salt, which is why India's chlor-alkali industry clusters in Gujarat.

Caustic soda (chemical) and Salt (commodity): 4 relationships.

How they are linked

1. Feedstock: brine

Physical flow · Strong · Salt to caustic soda

Electrolysis splits sodium chloride in brine into chlorine at one electrode and sodium hydroxide and hydrogen at the other, so salt supplies all the sodium in caustic soda.

  • about 1.5 t salt per tonne of caustic soda, from molecular weights before losses
  • about 90% share of US chemical feedstock salt used as brine, 2025

In the US most chemical salt is used as brine rather than as dry salt, and USGS notes that for most uses salt has no economic substitute. Each tonne of chlorine comes with about 1.13 t of caustic, so salt demand follows total chlor-alkali output rather than caustic demand alone.

Sources: European Commission JRC; USGS

2. Price link: feedstock

Cost and price · Weak · Both ways

Salt is a small share of caustic soda's operating cost while electricity dominates, so salt and caustic prices do not move together.

  • -0.10 monthly change correlation
  • 8 to 15% salt share of caustic soda operating cost in India
  • 50 to 65% electricity share of operating cost

The yearly correlation is also slightly negative, at -0.09. US salt in brine was valued at only about $11 a tonne in 2025, and with salt at 8 to 15% of operating cost in India, a 10% rise in salt cost adds only about 1 to 1.5% to operating cost. Caustic prices are driven instead by power costs, end-use demand and the chlorine balance of each plant.

Sources: Material Insights (World Bank, FRED, IMF data); USGS; AL Circle

3. Gujarat salt and chlor-alkali

Geography and ownership · High in India · Caustic capacity sits near coastal salt

Moving salt is costly relative to its value, so Indian chlor-alkali plants are built close to the solar salt works of the Gujarat coast.

  • 85% Gujarat share of India's salt output, 2021-22
  • 30 Mt India's salt production, 2025 estimate, third in the world
  • about 5.0 Mt India's caustic soda output, FY25

Much of India's chlor-alkali capacity is in Gujarat, where producers combine coastal salt with chemical infrastructure and nearby customers. The Indian Bureau of Mines names chlor-alkali makers as the major industrial consumers of salt; Indian industry used about 10.9 Mt in 2021-22.

Sources: USGS; AL Circle; Indian Bureau of Mines

4. Salt quality for membrane cells

Physical flow · Medium · Cell technology sets salt specification

Membrane cells, now used by almost all Indian caustic plants, need purified brine, so cleaner salt lowers purification cost and waste.

India's switch from mercury to membrane cells raised the quality bar for solar salt, and salt makers have acknowledged that much output falls short of chemical industry standards. Indian standard IS 797 specifies common salt for chemical industries, and washeries at large salt works are one route to meet it.

Sources: European Commission JRC; Indian Bureau of Mines; Business Standard; CARE Ratings

For investors

Key learnings

  1. Salt is a minor cost in caustic soda, so caustic margins track power prices and the chlorine balance, not salt prices.
  2. Captive brine wells or nearby salt works are a structural cost advantage, mainly through logistics and brine purification rather than salt price.
  3. In India, location in Gujarat and access to clean salt and captive power separate low-cost from high-cost producers.

What to track

  • Industrial power tariff and captive power cost: Power is the largest cost; a rise squeezes margins far more than salt (Monthly · state electricity regulators, company results)
  • ECU realisation (caustic plus chlorine value per unit): Falling ECU signals weak chlorine or caustic markets regardless of salt cost (Quarterly · company results, Alkali Manufacturers Association of India)
  • Industrial salt prices and monsoon impact on Gujarat salt works: Heavy rain cuts solar salt output and quality (Seasonal · Salt Commissioner, Indian Bureau of Mines)

For policymakers

Key learnings

  1. India's chlor-alkali industry depends on one state for most of its salt, so weather or land-use changes on the Gujarat coast are a supply risk.
  2. Better salt quality, through washeries and standards, lowers purification costs and waste for membrane plants.
  3. Power policy, not salt policy, decides the competitiveness of Indian caustic soda.

What to track

  • Salt production by state: A falling Gujarat output warns of feedstock tightness (Annual · Indian Bureau of Mines, Salt Commissioner)
  • Caustic soda imports and exports: Shows whether domestic capacity, built on local salt, meets demand (Monthly · Department of Commerce trade data)

India

India is the world's third largest salt producer, with about 85% of output from Gujarat, and chlor-alkali makers, much of whose capacity is in Gujarat, are the country's major industrial salt consumers.

Sources

  1. Price correlation, Material Insights, Material Insights (World Bank, FRED, IMF data)
  2. Best Available Techniques (BAT) Reference Document for the Production of Chlor-alkali, European Commission JRC (2014)
  3. Mineral Commodity Summaries 2026: Salt, USGS (2026)
  4. Caustic soda plant setup in India: how aluminium growth is reshaping demand, costs and opportunities, AL Circle (2025)
  5. Indian Minerals Yearbook 2022: Salt, Indian Bureau of Mines (2023)
  6. Industrial salt makers trying to upgrade tech, quality, Business Standard (2016)
  7. Caustic-chlorine industry in India: preparing for a sustainable rebound, CARE Ratings (2021)