Greensand Process Removes Iron, Manganese, Arsenic from Groundwater
In the years prior to World War II, researchers in the water
treatment field working with well-known chemical theories of oxidation and
reduction sought and developed a basic technology of manufacturing manganese
greensand from the mineral glauconite.
Manganese greensand is a specially processed medium for
iron, manganese, and hydrogen sulphide removal. This premium non-proprietary
filter medium is processed from glauconitic greensand on which a shiny, hard
finite thickness manganese oxide coating is formed and is firmly attached on
every grain by a controlled process.
The Greensand Process
This process utilizes the ion exchange properties of
greensand to form a manganese base material which is converted to manganese
oxides by oxidation with potassium permanganate. The material has a high
buffering or oxidation-reduction capacity due to the well-defined manganese
oxide coating. The manganese greensand can oxidize over 300 grains of manganese
per cubic foot or reduce over 1 oz. of potassium permanganate per cubic foot.
The grains of manganese greensand are of both the size and
shape to capture the fine precipitates of iron and manganese which pass through
the upper coarse anthracite layer during normal service conditions.
A true manganese greensand process requires no detention
time, no filter media, no high concentration of chlorine, and no sulphur
Manganese greensand is catalytic by nature and is not
soluble. There is no increase in the total dissolved solids of the treated
water, and it is not necessary to backwash manganese greensand every time the
well pump starts up.
The manganese greensand process has been used in the United
States since the 1950s. During the early years of its use, Hungerford &
Terry, Inc. of Clayton, New Jersey, worked to improve the process and
eventually developed the Ferrosand® CR Process, patented in 1965.
The Ferrosand Filter has been used since then by thousands
of municipalities and industrial customers worldwide.
Ferrosand Filter Media is manufactured to exact
specifications to ensure the complete oxidation of soluble iron, manganese, and
arsenic using stoichiometric quantities of oxidizing agents, without the need
for long reaction times or elevated pH levels. (For arsenic removal, a prefeed
of ferric chloride may be required.)
As a filter media it operates on the chemical principal of
oxidation and reduction, and the well known catalytic effects of manganese
A major benefit of Ferrosand, attributed to its unique
chemical properties, is that it can be used in two distinct methods of
operation. This allows for flexibility in the design of the water treating
equipment, with specific features tailored to the raw water characteristics.
Two Methods of Design, Operation
Ferrosand CR for Iron Removal --
The Ferrosand Continuous Regeneration (CR) process is used
primarily when iron removal is the objective, with or without the presence of
manganese. For more than 25 years in thousands of installations, this
technology has proven to be the most cost effective design when iron
predominates in the raw water.
The CR method uses a continuous pre-feed of potassium
permanganate (KMnO4) or a combination of chlorine (CL2) and KMnO4 to the raw
water prior to contacting the Ferrosand Filter. Soluble iron and manganese are
oxidized to the insoluble form and filtered out by a dual media anthracite /
Due to the unique chemical and physical properties of the
Ferrosand, attributable to the multivalent manganese oxide coating covering the
greensand grains, iron and manganese are removed to levels required by the Safe
Water Drinking Act or process requirements.
Manganese oxide has a well known catalytic effect on the
oxidation of soluble iron and manganese, and also provides a redox buffer
capable of either oxidizing remaining traces of iron and manganese, or reducing
excess KMnO4 as required.
This not only ensures the consistent removal of iron and manganese,
but also maintains the Ferrosand in a regenerated state, without the need for
batch KMnO4 regeneration.
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Ferrosand IR for Manganese Removal --
For groundwaters containing only manganese, or manganese
with lesser amounts of iron, the Intermittent Regeneration (IR) process may be
in order. It allows for extended run lengths with a minimum amount of head loss
during the filter run. In the IR process, a filter bed of Ferrosand is
periodically regenerated with a solution of KMnO4. The frequency of regeneration
is contingent upon the concentration of raw water manga-nese and the volume of
During the service cycle, manganese is removed by utilizing
the oxidative capacity of the Ferrosand. Oxidation of the soluble manganese
occurs directly on the Ferrosand grains, becoming an integral part of the
manganese oxide coating.
To prevent fouling of the Ferrosand by direct oxidation of
soluble iron on the grains, varying amounts of accompanying iron should be
oxidized using prechlorination prior to contacting the Ferrosand bed. Normally
an IR filter will be designed with a bed consisting entirely of Ferrosand.
However, depending on the concentration of iron in the raw
water, a dual media anthracite / Ferrosand bed may be specified.
For more information, phone Hungerford & Terry, Inc. at