ABOUT PHOSLOCK

Corporate Information

Phoslock Water Solutions Ltd (PWS) is an Australian public company listed on the Australian Stock Exchange (ASX). For information on PWS please refer to Recent ASX Announcements and Annual Reports.

Phoslock trades on the ASX under the ticker symbol "PHK".

PWS owns the Patents and global Trade Mark for ‘Phoslock’.

Phoslock is a modified clay product which removes phosphorus (Filterable Reactive Phosphorus – FRP or Soluble Reactive Phosphorus - SRP) from the water column and sediment pore water of water bodies.

Phoslock was invented and developed by the Commonwealth Scientific & Industrial Research Organisation (CSIRO), Australia's national scientific organization which has been dedicated to the practical application of knowledge and science for society and industry since 1928 and today ranks in the top one percent of world research bodies in twelve of its twenty-two research fields.

PWS manufactures Phoslock at its joint venture manufacturing operation near Kunming, China.

What Is Phoslock?

This page explains what Phoslock is, how it works and what its benefits are.

Phoslock is bentonite which has been modified through the introduction of the rare earth element lanthanum into its clay structure.

During the manufacture of Phoslock, lanthanum cations are exchanged onto the charged surface of the bentonite clay.  As the lanthanum ions are electrostatically bound to the bentonite, they will not readily disassociate from the clay, but are still able to react chemically with phosphate anions with which they come into contact.

Phoslock is manufactured as a dry granule but applied to the surface of a water body as a slurry, usually using in situ water. As the slurry moves down through the water column, up to 95% of the phosphate it encounters is adsorbed onto the surface of the clay.

How does Phoslock work?

Phoslock works by utilizing the ability of lanthanum to react with phosphate. Removal of phosphate by lanthanum is highly efficient and has a molar ratio of 1:1.

La3+ + PO43- => LaPO4

When Phoslock is applied to a water body, the lanthanum that has been adsorbed onto the charged surface of the clay will either react with any phosphate ions in the water column or sediment pore water or, in the absence of phosphate, stay locked within the bentonite structure.

Lanthanum phosphate is analogous to a highly insoluble, naturally occurring mineral known as rhabdophane.  Lanthanum is also present in the sediments of many lakes, with typical background concentrations of around 40 mg/kg dry weight. 

Click here for more information on bentonite and lanthanum.

How does Phoslock work within a water body?

Phoslock granules are generally mixed with in situ water and applied to a water body as a slurry.  As the slurry settles, phosphate anions in the water column are bound to the lanthanum cations contained within the bentonite clay.  Once Phoslock has settled on the sediment water interface, it forms a thin layer, usually less than 1 mm in thickness. As long as sufficient binding sites remain on the clay, this layer continues to remove any phosphorus that would normally be released from the sediment into the water column when anoxic conditions develop.

Once phosphorus is bound to Phoslock, it is no longer bioavailable for use by algae for assimilation and growth.  This lack of nutrients in the water body has a direct impact on the ability of algae to proliferate.

Phoslock operates over a wide pH range (4-11) and binds phosphate even under anoxic conditions.

How much phosphate does Phoslock remove?

One tonne of Phoslock is capable of removing 34 kg of phosphate (PO₄) or 11 kg of phosphorus (P).

Phoslock and algal growth

Phosphate is an important food source of algae (particularly blue green algae).  By removing phosphate from the water column and preventing its release from sediments, Phoslock essentially deprives algae of an important food source and the proliferation of algae, particularly blue green algae, is reduced.

Both nitrogen and phosphorus are important nutrients for algal growth, however the growth of blue green algae is generally not limited by the concentration of nitrogen as many species of blue green algae can fix and store nitrogen from the atmosphere.  The proliferation of blue green algae in a water body is related to the competitive advantage they have over other phytoplankton groups (such as diatoms and green algae) when excess phosphorus is available in the water. 

The reduction of phosphate levels in a water body and its sediments through an application of Phoslock will therefore result in a significant reduction of blue green algae and the restoration of healthy ecological conditions which favour the growth of diatoms, green algae and macrophytes.

 

Benefits of Phoslock

Phoslock offers a wide range of benefits over other methods of reducing phosphorus concentrations in lakes and reservoirs.  The combination of these benefits makes Phoslock a unique and innovative solution to eutrophication control. 

Some of the most important benefits of Phoslock include:

Reduction of phosphate

The ability of Phoslock to reduce phosphate to levels close to or below standard detection limits (< 10 µg/L) has been well demonstrated in a large number of both laboratory and field applications.  Importantly, dosages can also adjusted to achieve phosphorus concentrations that fall within a particular target range (e.g. 20-30 µg/L).  This approach is used when it is necessary to reduce phosphorus concentrations to levels that are sufficiently low to prevent blooms of blue green algae but high enough to ensure that the natural level of productivity in the system is retained.

Rapid uptake of phosphate

The kinetic uptake of phosphate by Phoslock varies to some degree according to water chemistry, however in most situations, more than 90% of available phosphate is bound within three hours of an application of Phoslock.

Eco-toxicological safety

Many eco-toxicity tests have been undertaken on a wide range of test species by a variety of independent academic and governmental research institutions over the past ten years.  Collectively, these reports demonstrate that Phoslock has a very low toxicity and is safe to use in all naturally occurring environmental conditions at the recommended dosages.  A detailed overview of these studies has been produced by Phoslock Water Solutions' Technical Team and can be downloaded from the Eco-Toxicity Assessment page.

In addition, unlike other methods of binding phosphate (such as iron and aluminium salts), an application of Phoslock will have no effect on either the pH or the conductivity of the water body. 

Stability under varying conditions

Unlike other methods that could be used to immobilize phosphorus in water and sediments, Phoslock is insensitive to the range of redox, temperature and pH conditions that are naturally found in lakes and reservoirs.  Furthermore, buffering is not required prior to an application.

Resistance to resuspension

Several studies have been conducted to determine the resistence of a Phoslock sediment capping to resuspension at different flow velocities. All studies have shown that Phoslock has substantially higher resistance to resuspension than aluminium or iron salts, which can also be used to immobilize phosphorus in sediments. This is not surprising given that the density of Phoslock is much higher than flocculants and highlights the suitability of Phoslock for use, even in shallow lakes.

Long term effect

Following the application of Phoslock to a water body, any phosphate that has reacted with the lanthanum in the clay will remain permanently bound.  Furthermore, any lanthanum sites in the clay matrix that have not reacted with phosphate remain active and will continue to bind phosphate (from both external and internal sources) until saturated.  This means that an application of Phoslock can be designed to achieve a sustained reduction in phosphate levels.