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The Raw Materials – Seawater & Limestone

The two main raw materials are seawater and limestone (Calcium Carbonate, CaCO3). There is also significant energy input into the process in the form of Natural Gas, Petroleum Coke, Heavy Fuel Oil and Electricity.

Seawater contains approximately 3.5% dissolved salts, of which about 0.5% are soluble Magnesium Chloride (MgCl2) and Magnesium Sulphate (MgSO4) salts. Approximately 500 Tonnes of seawater are required to produce 1 Tonne of Magnesium Oxide (MgO).

Seawater is collected from the estuary of the River Boyne and stored in a large reservoir (left) from where it is pumped to the factory, located a couple of kilometers upstream. Once in the factory, the seawater is degassed to remove hardness before being transferred to the reactor.

High Purity Limestone comes from local quarries, located about 8km southwest of the plant. The limestone is crushed, graded and transported to the production plant, where it is calcined (high temperature firing) at approximately 1600°C in a rotary kiln to convert it to quicklime (Calcium Oxide, CaO).  The chemical reaction is given by the following equation:

The resulting quicklime is then mixed with freshwater and converted to lime slurry (Calcium Hydroxide, Ca(OH)2) in a highly exothermic reaction known as hydration or slaking:

Precipitation of Magnesium Hydroxide

After slaking, the lime slurry is pumped to the reactor where it reacts with the degassed seawater. Precipitation of Magnesium Hydroxide (Mg(OH)2) occurs instantaneously and is described by the following equation:

After the reactor, the Magnesium Hydroxide slurry flows to two large tanks known as primary thickeners, where the Magnesium Hydroxide crystals are settled and thickened. 

Filtration and Washing

The settled Magnesium Hydroxide slurry is pumped to two secondary thickeners and then to rotary vacuum filters in the multiple hearth furnace (MHF) building. Here the slurry is filtered and washed with freshwater and the filtercake is sent to two pressure filters, which squeeze more water from the cake to increase the solids content further and reduce the amount of water going onto the next stage of the process – magnesia calcination.

Calcination and Briquetting

Premier Periclase operates two natural gas-fired multiple hearth furnaces in parallel. Each furnace has sixteen hearths and the Magnesium Hydroxide filtercake is pushed from one floor to the next in a zigzag pattern down through the furnace.

Excess moisture is boiled off in the first six hearths, while in the middle hearths (#7 - #12) the Magnesium Hydroxide is thermally decomposed at temperatures in the region of 1000°C to Magnesium Oxide (MgO). The thermal decomposition reaction is represented by the following chemical equation:

This material, now known as Caustic Magnesia (Magnesium Oxide, MgO), is cooled to 300 - 350°C in the lower hearths and then pressed into stick shaped pellets or green briquettes. These pellets are the feed for the final stage of the process, known as sintering.


Sintering in the Shaft Kilns

The last high temperature stage in the process is sintering and it is done in two vertical natural gas-fired shaft kilns. Each kiln has a rated output of 50,000 Tonnes per annum.



Green pellets are fed to the shaft kilns, where they are heated to temperatures in the region of 2300°C. The intense heat encourages the Magnesia crystals to grow and the briquettes begin to shrink as the bulk density increases. The final product, Periclase (also known as Sintermagnesia or Deadburned Magnesia), is a very dense, chemically inert, refractory grade sintermagnesia.


Storage and Despatch

After sintering, the periclase is transported to a covered storage warehouse from where it is sent to the wharf for bulk shipment or to the bagging plant for smaller loads in bulk containers.

The production process is illustrated in the attached flowsheet
Premier Periclase, Boyne Road, Drogheda, Co. Louth, Ireland
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Premier Periclase Limited, Registration Number 59188, Registered Office, Boyne Road, Drogheda, County Louth