Demin Plants

Demineralization (Demin) Plants

Natural occurring water contains many dissolved solids in dilute forms which are usually various types of salts. These solids are known as total dissolved solids (TDS). Demineralization is the process of removing nearly all dissolved solids and mineral ions from water.

In industrial water treatment, demineralization refers to the removal of dissolved solids from feed water and process streams. By definition, demineralization is the near-total removal of inorganic salts from water. In most industrial process water treatment applications, this is accomplished through ion exchange.

What is a Demin Plant?

A demin plant is a type of water purification plant. A Demin plant refers to any water treatment process or technology that near total removal of ionic mineral contaminants. Demin water plants are typically done with ion exchange or reverse osmosis, depending on the facility’s needs, demineralization can provide near-total removal of ionic mineral contaminants.

Demin water is used widely for industrial and scientific purposes such as in laboratory applications and testing, computer chip manufacturing, lead-acid batteries, cooling systems, high pressure boiler feed, laser cutting, steam irons and steam raising, pharmaceutical manufacturing, cosmetics, aquariums and fire extinguishers.

How does a demin plant work?

A demin plant typically consists of two vessels; one containing cation and the other containing anion exchange resins. Raw water enters first through the cation resin, where mineral contaminants are replaced by hydrogen ions, and next through an anion resin, where mineral contaminants are replaced by hydroxyl ions, which combine with the hydrogen ions to form pure water. A demin plant then needs to be regenerated with hydrochloric acid and sodium hydroxide when necessary.

There is some flexibility in the configuration of a demineralization system in order to optimally meet various process conditions and purity goals. In designing a demineralization system, consideration should be given to changeability of the feed water, level of purity needed, system footprint, tolerance for ion leakage (in particular sodium and silica), and chemical feed requirements, among other factors.

What industries use demin plants?

Food and Beverage

Demineralized water is often used to sanitize containers and equipment. It is also used in certain food processing applications, even though membrane filtration is usually the technology used so organic material, bacteria and viruses can be eliminated.

Pharmaceuticals and Cosmetics

Deionized and distilled water are used in the manufacturing of pharmaceutical products and cosmetics in order to control product quality and safety.

Other industries

Demineralized water are both used for cleaning and rinsing applications across a wide variety of industries including chemical production, refineries, mining, as well as solvents in applications as diverse as electro coating, where they function as a carrier for paint solids or in research labs where they may be used to make a variety of solutions.

What are the main components of a demin plant?

The specific design and components of an ion exchange demineralization system can vary from one application to the next based on process conditions and composition of the stream to be treated.

1. The resin tanks

The resin tank is the chamber where the hard water is softened. The water supply line feeds the hard water into the tank. The water seeps through the bed of resin beads, depositing the water-hardening calcium and magnesium ions. The water exits the tank soft.

Allmech offers a range of FRP (Resin) tanks:

Please contact Allmech for technical advice on your demin plant requirements.

2. The control valves

Control valves are demand-initiated controllers, which allow demin plant units to be extremely efficient. The control valves have 5 main functions: Service, Backwash, Brine and slow rinse, Brine refill and Fast rinse.

Allmech is the sole agent for Runxin water treatment system valves in the South Africa. We supply a full range of manual and automatic filter and softener valves. The valves are reliable, easily available, user-friendly and cost effective.

The valves have proven to be more chemical resistant and robust than other brands on the market. Allmech is fully equipped to test, service and repair these valves locally.

3. The cation and anion tanks

The plant is requires cation and anion exchanger tanks. Allmech offers tanks ranging in size from 50 lts to 2000 lts.

4. The control board

The main purpose of the control panel is to receive the signals from different sensors as inputs and transform these input signals into understandable visual codes in order to assist human operators observing the overall performance of the plant.

What contaminants does demineralization remove?

Demineralization generally results in almost complete removal of minerals, and is typically reserved for applications requiring higher level of water purity, such as feed or makeup water for high pressure boilers, rinse water for food and beverage industries, or process streams used in electronics manufacturing. Below we have outlined the most common contaminants treated by demineralizers:


The cation resins within a demineralization system will exchange cations, or contaminants having a positive charge. Common cationic contaminants include:

  •  Calcium (Ca2+)
  •  Iron (Fe3+)
  •  Magnesium (Mg2+)
  •  Manganese (Mn2+)
  •  Potassium (K+)
  •  Sodium (Na+)


The anion resins within a demineralization system will exchange anions, or contaminants having a negative charge. Common anionic contaminants include:

  • Alkalinity (CO32-, HCO3–)
  • Chloride (Cl–)
  • Nitrate (NO3–)
  • Sulfates (SO42-)

What is the best method to use when you need to demineralize industrial process water?

The demineralization process is frequently accomplished by in-plant or exchange service deionizers, reverse osmosis or electro-deionization. There are several advantages to demineralizing water via membrane technologies or electrodeionization. These include eliminating the need for chemicals, reducing hazardous waste, and lowering maintenance costs.

Allmech is able to supply demin plants and uses up-to-date technology to ensure the best performance for our customers.