What is Phoslock

    Phoslock was developed in Australia by the Commonwealth Scientific and Industrial Research Organisation (CSIRO), to remove phosphates from water. The active element in Phoslock is lanthanum (a rare-earth element) which has a strong affinity to bind with phosphate. This forms an insoluble and biologically inert compound, Rhabdophane. Phoslock is comprised of 95% bentonite and 5% lanthanum. 


    It is manufactured through a controlled ion-exchange process whereby cations within the bentonite are exchanged with lanthanum cations. The result is that lanthanum held within the bentonite structure retains its ability to bind phosphate, but does not readily dissociate, i.e. will not form free ions in water. 

    Phoslock is manufactured as a dry granule which makes it easy to transport and store. 

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    How is Phoslock applied to a water body

    When used in lake restoration, Phoslock is usually added to a water body as a slurry. Phoslock is mixed with in-situ lake water and sprayed over the water’s surface. As Phoslock sinks, it strips phosphate from the water column. Once settled on the sediment, Phoslock continues to bind phosphate released from the sediment, until the lanthanum binding sites are saturated, at which point no further binding will take place. 
    See also: Application Methods

    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 which means that one ion of lanthanum will bind with one ion of phosphate. This binding forms the mineral Rhabdophane (an insoluble and biologically inert compound) which strips phosphate from the water.

    What happens to Phoslock when it has been applied?

    Once on the sediment, Phoslock, and the lanthanum phosphate within it, remain as in inert mineral component of the sediment. The nature of the bond between lanthanum and phosphate is such that it will not be broken under any naturally occurring pH range (pH 4-11). Even more importantly, the bond will not be broken under anoxic (low redox potential) conditions, which are prevalent in most lake sediments and many overlying waters. Most other phosphorus binders, especially those containing iron, will release phosphate under anoxic conditions.

    How much phosphate does Phoslock remove?

    One tonne of Phoslock is capable of removing 34 kg of phosphate (PO 4 ) or 11 kg of phosphorus. With this information and a knowledge of the amount of biologically available phosphorus in the water and surface sediments of a lake, it is possible to accurately calculate the Phoslock dose for a water body.
    See our FAQ section to find out more about Phoslock and its effects on the aquatic environment. 
    FAQs

    Considering an application of Phoslock? 

    Every lake is different and a range of information about the lake needs to be collected when considering a Phoslock treatment. For instance, it is important to determine the sources of excess nutrients to your water body; i.e. are the nutrients coming largely from internal sources (e.g. from phosphorus release from sediments) or from external sources (e.g. from diffuse or point sources in the catchment). This is critical to know as continued high external loads could impact the effectiveness of a Phoslock application.

    Water quality data is vital to understand each water body's unique story. Long-term water quality monitoring data is unfortunately rare for many water bodies but regular monitoring helps us understand what management options may be best if nutrient pollution and symptoms of eutrophication have become a problem, e.g. regular occurrences of algal blooms. Water quality monitoring data is also vital to help us understand if Phoslock is a suitable product to control nutrient pollution in a water body as there are many aspects that need to be considered before an application. 
    In addition to water quality sampling, sediment sampling is often needed to estimate how much phosphorus is potentially releasable under normal lake conditions. This information, along with other nutrient calculations is used to make an informed dose calculation for a Phoslock application. 

    Please get in touch if you are considering Phoslock to treat your water body or if you need further information. We can offer advice and create a pre-treatment assessment, estimated dose calculations and costings for your water body.
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