Magnetic Water Treatment

Abstract

Carbonates formed by heating water containing ≈120 mg(Ca)/l are characterized by X-ray diffraction and electron microscopy. Tests on 32 pairs of samples establish, at the 99.9% probability level, that drawing water through a static magnetic field (B≈0.1T, ∇B≈10 T/m) increases the aragonite/calcite ratio in the deposit. There is an incubation period of several hours, and memory of magnetic treatment extends beyond 200 h.

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1Manufactured by D-Fluid, Milan.
*Corresponding author. Tel.: #353-1-6081470; fax: #353-
1-6772941.
E-mail address: jcoey@tcd.ie (J.M.D. Coey)
Journal of Magnetism and Magnetic Materials 209 (2000) 71}74
Magnetic water treatment
J.M.D. Coey*, Stephen Cass
Physics Department, Trinity College, Dublin 2, Ireland
Abstract
Carbonates formed by heating water containing +120 mg(Ca)/l are characterized by X-ray di!raction and electron
microscopy. Tests on 32 pairs of samples establish, at the 99.9% probability level, that drawing water through a static
magnetic "eld (B+0.1T, +B+10 T/m) increases the aragonite/calcite ratio in the deposit. There is an incubation period
of several hours, and memory of magnetic treatment extends beyond 200 h. (2000 Elsevier Science B.V. All rights
reserved.
Keywords: Magnetic water treatment; Superparamagnetism; Permanent magnet applications
The limescale problem in hard water arises because the
solubility of CaCO3decreases with increasing temper-
ature [1]. Huge amounts of energy are wasted because
hard scale forms in boilers, heat exchangers and domestic
hot-water systems. Various magnetic, electromagnetic
and electrostatic devices purporting to control limescale
formation are sold worldwide for domestic and industrial
applications. Typical products incorporate arrangements
of permanent magnets; large magnet structures are in
daily use in industries ranging from brewing to hydro-
electric power generation. Belief in the bene"cial e!ects of
magnetic "elds on water has led to the sale of millions of
magnetic cups in China.
Despite its ubiquity, there is relatively little scienti"c
literature on magnetic water treatment. It is not clear
how, or even if, it works. Unlike chemical water soften-
ing, magnetic treatment should have no direct e!ect on
water chemistry (unless the magnets are in contact with
the water); yet, it is claimed to alter the morphology and
adhesion of calcium carbonate scale. Published data are
often contradictory. For example, there is some dispute
as to whether the deposits of calcium carbonate from
magnetically treated water are predominantly calcite or
aragonite. These are the two common natural forms of
CaCO3, with rhombohedral and othorhombic crystal
structures, respectively. Aragonite has the higher density,
and it is less prone to form hard scale. The e$cacity of
magnetic treatment is reported to last from tens of min-
utes to hundreds of hours. There is a review of the
literature by Baker and Judd [2].
These, and similar claims of a "eld e!ect on precipita-
tion of other salts, coagulation of colloids and wax
formation from crude oil, have been met with consider-
able scepticism, mainly because there is no obvious way
for a magnetic "eld to in#uence any of these processes.
Much of the irreproducibility of the data, and possibly
the e!ect itself, may result from inadequate control of
experimental conditions. Here, we set out to establish
whether or not any e!ect exists. We conducted blind tests
using identically treated pairs of samples, with and with-
out magnetic "eld. There is considerable variability in the
results, but our method allows us to answer the key
question, and to identify some relevant variables.
Two groups of experiments were conducted, each us-
ing di!erent water and a di!erent magnetic device. The
"rst was on groundwater drawn from a well sunk in
limestone in West County Dublin, Ireland. The water
could either be drawn through a plastic "lter assembly
containing a stack of Te#on-coated ferrite ring magnets1,
or bypass the magnet assembly. The water was sealed in
0304-8853/00/$ - see front matter (2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 8 8 5 3 ( 9 9 ) 0 0 6 4 8 - 4

Table 1
Analyses of untreated water (mg/l). The only signi"cant changes after magnetic treatment are shown in square brackets
Well water Mineral water Well water Mineral water
Na 6 15 SO315
Mg 24 16 NO20.05
K13NO
3
(0.01 9
Ca 132 114 Cl 23
Fe 2.49 [1.39] (0.01
Mn 0.46 [0.37] (0.01 pH 7.2 6.9
Zn 0.04 p(mS/m) 64.8
2Manufactured by San Huan, Peking.
Fig. 1. A set of data showing evolution of the aragonite ratio
A with incubation time t*in untreated water (#), treated water
(L) and the di!erence (d).
Fig. 2. Electron micrographs of carbonate deposits from un-
treated (left) and magnetically treated (right) mineral water.
1-l polythene bottles, and all tests were conducted blind.
The experimenter (SC) was unaware whether a particular
sample had been drawn through the magnetic device,
or through the bypass valve. The second group of
experiments was conducted on a commercial still mineral
water, which was simply poured out of its 500 ml bottle
with or without a 20 mm split-ring collar containing
Nd}Fe}B magnets2"tted around the neck of the bottle.
In each case the water was exposed to a maximum "eld of
+0.1 T, and a "eld gradient of +10 T/m. Analyses of
the water are given in Table 1. The only discernable
di!erence after magnetic treatment was a decrease in Fe
and Mn content of the well water, shown in square
brackets.
More than 100 samples were examined using a simple
protocol. Water was stored for a time t*before heating in
open 500 ml beakers at 803to form limescale. Scale was
collected on a fresh microscope slide at the bottom of the
beaker. All samples were examined by X-ray di!raction
using Cu Karadiation, and 14 of them were selected for
scanning electron microscopy and microprobe analysis.
The ratio of calcite to aragonite was evaluated by
measuring the ratio of three X-ray re#ections in the
region 253(2h(303. The peaks are calcite 104 and
aragonite 111 and 102. The quantity
A"(I111#I102 )/(I104 #I111 #I102)
gives an estimate of the fraction of calcium carbonate
present as aragonite.
The incubation time t*was varied from 0 to 200 h, and
the speed of #ow of water through the magnets was
varied from 0.04 to 1.2 m/s. Aranged from 0% to 100%.
No systematic in#uence of #owrate could be discerned,
but the data suggest a maturing e!ect when Aincreases
with t*for several hours, and that a signi"cant increase in
Apersists for as long as 200 h after magnetic treatment
(Fig. 1). Electron micrographs of carbonate deposits from
untreated (A"7%) and treated (A"54%) mineral
water are shown in Fig. 2. The long, acicular crystals
(+30]3]3lm3) are identi"ed as aragonite [3], where-
as the equiaxed crystals (+4lm) are calcite. Typical
microanalyses are shown in Table 2. The main di!erence
in composition is that the acicular crystals contain less
Mg and no Mn. Neither contains detectable amounts of
Fe ((0.1 wt%).
A comparison of Afor 32 pairs of samples, each includ-
ing an untreated control is summarized in Table 3. It is
72 J.M.D. Coey, S. Cass /Journal of Magnetism and Magnetic Materials 209 (2000) 71}74

Table 2
Typical microprobe analyses of calcite and aragonite from min-
eral water and well water (at%)
Well water Mineral water
Calcite Aragonite Calcite Aragonite
Na 1.5 2.8 3.1 0.8
K 0.3 0.2 1.0 0.1
Mg 3.7 1.0 3.0 }
Ca 90.7 95.8 90.7 99.1
Mn 3.2 }} }
Cl }}1.7 }
S 0.6 0.2 0.5 }
Table 3
E!ect of magnetic treatment; numbers of tests in which aragon-
ite increased (C), decreased (B) or did not change (%)
dACA%ABSAT6/ SAT53
Well water 20 14 3 3 0.31 0.50
Mineral water 12 11 1 0 0.30 0.58
Total 32 25 4 3 0.31 0.53
evident that the average SAT53 tends to be greater in
treated samples of both waters, although standard devi-
ations are large because of the variability of the data
being averaged (di!erent #ow rates and incubation
times). The null hypothesis, that magnetic treatment has
no e!ect on A, can be tested directly on the pairs of data
on treated and untreated samples where all other condi-
tions remained the same. The probability of this is 4% for
the well water, and 0.3% for the mineral water. Taking
both data sets together, we deduce that magnetic treat-
ment increases the amount of aragonite in the carbonate
deposits, at the 99.9% probability level (3.4 pcon"dence
level).
In order to try to understand the mechanism, we recall
that the reaction
Ca2`(aq)#2HCO~
3(aq)
PCaCO3(s)#H2O(l)#CO2(aq),
has an associated Gibbs free energy *G"!24 kJ/mol,
but the free energy di!erence between pure calcite and
aragonite at 253C at 1 bar is only !1 kJ/mol
(+120 K/ion) [1]. Calcite has the lower free energy
under ambient conditions; aragonite has the lower en-
thalpy, but also the lower entropy. Despite its metastabil-
ity, aragonite formation is favoured at lower evaporation
rates and higher temperatures [4]. Minute concentra-
tions of cations such as Fe2`[5] and Zn2`[6] can
in#uence nucleation. Our data indicate that the magnetic
"eld somehow promotes nucleation of aragonite as the
water #ows past the magnets; the nuclei are stable for
hundreds of hours and they grow into the observed
crystals when the water is heated to supersaturation.
From the volume of the aragonite crystallites,
+3]10~16 m3, the number of nuclei is estimated to be
+108/l.
The problem is to explain how a magnetic "eld in#uen-
ces nucleation, and why it favours aragonite. Conceiv-
ably, the "eld might:
(i) lower the energy of a nucleus because of a di!erence
in susceptibility with the surroundings. Microprobe anal-
ysis found no iron or manganese in the aragonite crystals,
but even assuming that S"5
2ions are present at the
1 at% level in nuclei, energies involved in a 0.1 T "eld are
only of the order of 10~2 J/mol.
(ii) in#uence clusters of iron or manganese hydroxide
that act as heterogenous nucleation centres. For example,
d@FeOOH has a plate-like morphology with a net mo-
ment when an odd number of ferromagnetic layers are
coupled antiferromagnetically [7]. The energy (1
2)MB of
superparamagnetic clusters will be of the order of
1 J/mol.
(iii) modify the local ionic concentrations via the
Lorentz force q*]B. By analogy with the Hall e!ect,
assuming v"1 m/s and B"0.1 T, the nonelectrostatic
"eld of 0.1 V/m is associated with a surface charge den-
sity of 10~11 C/m2. This corresponds to an extra ionic
concentration in the micromolar range, provided the
charge is concentrated in a surface layer 1 nm thick. This
is still three orders of magnitude less than the Ca concen-
tration, but it is comparable to the concentrations of
OH~and HCO~
3, which limit formation of the CO2~
3
ion [1]. Statistical #uctuations or turbulence may en-
hance it locally.
In conclusion, we have established that a magnetic
"eld e!ect exists. Passing water through a magnetic "eld
subsequently favours formation of aragonite rather then
calcite in our experiments, and the in#uence of the treat-
ment persists for more than two hundred hours. Further
experiments on ultra-pure calcium carbonate solutions
are needed to test the hypotheses regarding the mecha-
nism by which the magnetic "eld produces the e!ect.
Acknowledgements
The work was supported by Forbairt, the Irish science
and technology agency (SC/96/771). We are grateful to
Dr. Vincent Young for the water analyses and to Dr.
Joseph Taillet for a helpful discussion.
J.M.D. Coey, S. Cass /Journal of Magnetism and Magnetic Materials 209 (2000) 71}74 73

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