CHAPTER V
Isolation of Potassium Chloride (KCl) from banana plant (Musa
balbisiana)fibre ash
V. 1 Introduction
The chemical compound potassium chloride (KCl) is a white or colorless,
odorless vitreous crystal in its pure state. Potassium chloride crystals are face-centered
cubic. It was historically known as “muriate of potash”, this name is occasionally still
encountered in association with its use as a fertilizer. KCl is used not only as a fertilizer
but also in medicine, food processing and scientific application etc.The colour of
potassium chloride varies from pink to red to white depending on the mining and
recovery process used. The melting point and solubility of potassium chloride are as
follows.1
Melting point
= 770°C
Solubility in water
= 281 gL-1 (at 0 ℃)
= 344 gL-1(at 20 ℃)
= 567 gL-1 (at 100 ℃)
V.1.1 Uses of potassium chloride
V.1.1.1As fertilizers
Potassium
is
the
third
major
plant
and
crop
nutrient
after nitrogen and phosphorus. It has been used since antiquity as a soil fertilizer.2
Agricultural fertilizers consume 95% of global potassium chemical production and
about 90% of this potassium is supplied as KCl.3Potash is important for agriculture
because it improves water retention, yield, nutrient value, taste, colour, texture and
disease resistance of food crops.4 Moreover plants require potassium for photosynthesis,
osmotic regulation and the activation of enzyme systems.5Sufficient potassium results in
stronger straw of cereal crops and assists in seed filling. Potassium deficiency in cereal
crops results in reduced growth, delayed maturity, lodging caused by weak straw, and
low bushel weight.6It has wide application to fruit and vegetables, rice, wheat andother
125
grains, sugar, corn, soybeans, palm oil and cotton, all of which benefit from the
nutrient’s quality enhancing properties.7The concentration of potassium chloride in
muriate of potash is expressed as the corresponding concentration of potassium oxide
(K2O), i.e., the concentration of potassium oxide that there would be if the potassium
were present as its oxide instead of as its chloride. Thus, muriate of potash that contains
(typically) 80% or 97% KCl by weight is said to contain 50% or 60% K2O, respectively
V.1.1.2 As deicer
Potassium chloride is used as a deicer for clearing snow and ice from roads,
drives, and the entries to buildings. Other chemicals used as ice smelters are rock salt
(NaCl), calcium chloride, magnesium chloride, calcium magnesium acetate and urea.
The best product in terms of limiting corrosion is the acetate, but it is effective only
down to -6 or -7 ℃ but potassium chloride is effective down to -11°C, lower than the
other chloride salts and urea. On the other hand, though it is equally corrosive to metals,
but does not chemically attack concrete. The main advantage of KCl over the other
melting materials is that the K has a fertilizing value for grass, trees and shrubs on the
roadside.8
V.1.1.3 As water softener
Potassium chloride is used to regenerate the ion exchange resins used to treat
hard waters, working on the principle of ion exchange. A synthetic resin bed (zeolite) is
charged with Na or K ions by regeneration with NaCl or KCl. Calcium and Mg in the
hard water exchange with the Na or K to give soft water, free from Ca and Mg. In
addition, Fe and Mn, which are contaminants in drinking waters, can be removed by the
same process. Using KCl rather than NaCl is more environmentally friendly.9 This is
because the size of the hydrated K ion is 40% smaller than that of the hydrated Na ion
so the K ion is more effective at exchanging with Ca and Mg. Thus less KCl has to be
used and so less Cl is discharged to the environment. KCl can reduce the amount of
chlorides discharged to septic or sewage systems by as much as 20%.10 Moreover using
potassium chloride raises levels of potassium in drinking water reducing the risk of
hypokalemia (low potassium). In agricultural settings, potassium in the water supply
126
acts as an important food source for plants and reduces the amount of sodium in the
drinking water of animals.
V.1.1.4 Industrial uses
Potassium chloride is important in industrialized economies; about 4-5% of
potash production is used in industrial applications.11Industrial potash should contain at
least 62% K2O.Potassium chloride is used in aluminium recycling, by the chloralkali
industry to produce potassium hydroxide, in metal electroplating, oil-well drilling fluid,
snow and ice melting, steel heat-treating and water softening. Potassium hydroxide
(KOH), also known as caustic potash, is the largest volume potassium product for nonfertilizer use. It is produced by the electrolysis of industrial KCl and is widely used for
manufacturing soaps, detergents, grease, catalysts, synthetic rubber, matches, dyes and
insecticides. Caustic potash is also used as a liquid fertilizer and as an ingredient in
alkaline batteries and photographic film processing chemicals. It is a raw material in the
production of various K salts, mainly potassium carbonates, citrates, silicates,
acetates,several forms of potassium phosphate, many other potassic chemicals, and soap
manufacturing. Potassium carbonate confers excellent clarity to glass thus is used for
most fine optical lenses, eyeglasses, fine crystal, glassware, chinaware and TV tubes,
fluorescent lamps, textile dyes and pigments.12 Potassium bicarbonate is used to
produce animal feed supplements, cement, fire extinguishers, food products,
photographic chemicals, and textiles. It is also used in brewing beer, pharmaceutical
preparations, and as a catalyst for synthetic rubber manufacturing. Potash-derived
compounds and salts are also used in the production of metal fluxes, cured meats,
tempered steel, paper fumigants, case hardened steel, bleaching agents, baking powder,
cream of tartar and beverages.These non-fertilizer uses have accounted for about 15%
of annual potash consumption in the United States.13
127
Worldwide, industrial KCl is estimated14 to be used as follows:
Detergents and Soaps
30-35%
glass and ceramics
25-28%
textiles and dyes
20-22%
chemicals and drugs,
13-15%
Other uses
7-5%.
V.1.1.5 As fire extinguishing agent
Potassium chloride was once used as a fire extinguishing agent, used in portable
and wheeled fire extinguishers. Known as Super-K dry chemical, it was more effective
than sodium bicarbonate-based dry chemicals and was compatible with protein foam.
This agent fell out of favor with the introduction of potassium bicarbonate (Purple-K)
dry chemical in the late 1960s, which was much less corrosive and more effective. It is
rated for B and C fires.These two fire classes include flammable or combustible liquid
or gas and electrical equipment which are involve in the fire as fuel in American fire
classification system.
V.1.1.6 Optical uses
Potassium chloride is also an optical crystal with a wide transmission range from
210 nm to 20 µm. While cheap, KCl crystal is hygroscopic. This limits its application to
protected environments or short term uses such as prototyping. Exposed to free air, KCl
optics will "rot". Whereas KCl components were formerly used for infrared optics, it
has been entirely replaced by much tougher crystals like ZnSe.
V.1.1.7 Health Uses
Low potassium (hypokalemia) refers to a lower than normal level (3.5 to 5.0
mM per liter) of potassium in bloodstream.15 Potassium chloride in the medical field is
used to treat hypokalemia,16 a condition in which the potassium levels in the blood have
dropped due to illness or reaction with certain medications, or from excess vomiting
and/or diarrhea. Mild hypokalemia is often part of a poor nutritional intake, potassium
containing foods may be recommended, such as leafy green vegetables, tomatoes, citrus
128
fruits, oranges or bananas.17 Some cardiac surgery procedures cannot be carried out on
the beating heart. For these procedures, the surgical team will bypass the heart with a
heart-lung machine and inject potassium chloride into the heart muscle to stop the
heartbeat.
V.1.1.8 As salt substitute
Potassium chloride is used as a salt (NaCl) alternative for people looking to cut
back their salt intake, either on its own, or in a mixture with sodium chloride. Salt
(sodium chloride) is needed by all known animals and plants in small quantities but
harmful in excess. An individual can consume not more than 1500–2300 mg of sodium
(3750–5750 mg of salt) per day depending on age.18 Eating too much salty food causes
hypertension, abnormal heart development, kidney disorder, dehydration and swelling,
digestive diseases, electrolyte and hormone imbalance.19Among other ways to flavor
our food and limit sodium intake for lowering blood pressure and other physiological
anomalies, salt substitutes is one option.Salt substitutes replace some or all of the
sodium with potassium chloride in the salt. The downside of using potassium chloride
as a salt substitute is that it is also harmful when consumed in large quantities. People
who suffer from kidney problems can find it difficult to expel large quantities of
potassium chloride form their bodies.20
V.1.1.9 Lethal Injection
Lethal injection is used in many states of the U.S. as a form of capital
punishment. Three chemicals are administered in lethal injection executions. The lethal
effects of potassium chloride overdoses have led to its use in lethal injection, as the third
of a three-drug combination: sodium thiopental, pancuronium bromide and potassium
chloride. Sodium thiopental is used as a fast-acting anesthetic; pancuronium bromide is
then administered as a paralyzing agent before potassium chloride is used to stop the
heart while producing extreme pain.21 Additionally, KCl is used (albeit rarely) in fetal
intracardiac injections in second- and third-trimester induced abortions.22
Jack
Kevorkian's thanatron machine injected a lethal dose of potassium chloride into the
patient, which caused the heart to stop functioning, after a sodium thiopental-induced
coma was achieved.23
129
V.1.1.10Other applications
Potassium chloride is sometimes used in water as a completion fluid in
petroleum and natural gas operations. KCl is useful as a beta radiation source for
calibration of radiation monitoring equipment, because natural potassium contains
0.0118% of the isotope 40K. One kilogram of KCl yields 16350 becquerels of radiation
consisting of 89.28% beta and 10.72% gamma with 1.46083 MeV.24 Along with sodium
chloride and lithium chloride, potassium chloride is used as a flux for the gas welding of
aluminum. It is also used in various brands of bottled water.
V.2 Materials and methods
V.2.1 Materials
Materialof this experiment was banana pseudo-stem fibre ash. The required ash
was prepared from the banana pseudo-stem fibre following the procedure as described
in the section IV.2.1. Only leaf sheath fibre was selected for this experiment as larger
quantity of leaf sheath fibre has been obtained compared to tender core fibre from the
same pseudo-stem.
V.2.2 Methodology
V.2.2.1 Preparation of water extract
A mixture of 25 g of dry ash and 500 ml distilled water in a 1000 ml conical
flask was magnetically stirred for one hour and filtered. The filtrate was used for the
isolation of potassium chloride. (cf. section IV.2.2.1)
V.2.2.2 Preparation ofsalt substitute
The chemical and spectroscopic estimation done on the water extract of fibre
ashdescribed in the Chapter IV. The pH of the solution is 10.9. It may due to the
presence of metallic carbonate and hydroxide in the solution. The solution was treated
with dilute hydrochloric acid drop wise just to neutralize the solution. The neutralization
point was detected by observing the pH (pH=7). Now the solution was heated to
evaporate slowly until a solid product was obtained.A white crystalline solid was
obtained and which was then allowed to cool in a desiccator and weighed. For the
estimation of chloride ion in the solid, a weighed amount of solid was dissolved in
130
distilled water and applied the procedure for chloride estimation as described in section
II.3.3.3. Other ions present in the solid were estimated by calculating back the results
obtained from water extract of fibre ash.
V.2.2.3 Isolation of potassium chloride
The solid obtained from aqueous extract of fibre ash after neutralization by
dilute HCl (Section V.2.2.2), may be used either as salt alternative or to obtain KCl of
higher grade. For the latter, fractional crystallization method was applied.
1000 ml water extract from 50 g ash of leaf sheath fibre of banana plant (Musa
balbisiana) was prepared and neutralized by 1 M HCl following the procedure as
described in the section V.2.2.1. But in this case HCl was added slight excess to make
the solution acidic i.e., pH should be less than 7, so that the crystallization of KCl take
place easily. The slightly acidic solution was taken in a 1000 ml beaker and evaporated
by heating slowly on an electric hot plate. When the volume became 50 ml, the whole
solution was transferred to another pre weighed 100 ml beaker and heated againso that
crystallization can take place successfully. The volume of the solution was reduced to
18 ml and kept it for cooling, without disturbing. At this stage the ionic product of K+
and Cl- ions can cross the solubility product (21.7) of it but the ionic product of Na+ and
Cl- cannot cross its solubility product (37.3). So, KCl could be precipitated at this
concentration. After half an hour, a white crystal was observed. The supernatant liquid
was separated by decantation; white crystal was obtained at the bottom of the beaker.
The crystals were dried by spreading over a filter paper and then keeping it in a
desiccator. The crystals were removedand weighed. The solid so obtained was termed as
first crop and its weight was 8.1142 g (47.72% of the total product).
The supernatant liquid was transferred to a pre-weighed 100 ml beaker and
evaporated to dryness in a hot plate. The solid obtained in the beaker was allowed to
cool in a desiccator and weighed. The solid mass obtained was termed as second crop
and its weight was 8.8910 g. (52.28% of total product)
The first crop of the solid (8.1142 g) was then dissolved in distilled water in a
500 ml volumetric flask and made the volume up to the mark with distilled water and
estimated the constituents with the help of chemical and spectrometric methods
applying same procedure as described in the section IV.2.2.3.
131
Similarly, the second crop (8.8910 g) was also dissolved in 500 ml distilled
water in a 500 ml volumetric flask and estimated quantitatively the constituents by
chemical and spectrometric methods applying same procedure as in the case of first
crop. The results for both first and second crops are given in the Table V.6 to Table V.9.
V.3 Results and discussion
The aqueous extract of the ash derived from the fibres of banana plant pseudostem is highly alkaline with pH measuring 10.9. The solution, after careful
neutralization with dilute HCl followed by evaporation yield a white crystalline product.
pH of the water extract of fibre ash = 10.9
The weight of the white solid
= 8.5026 g
Table V.1: Composition of the white crystalline product
Entry
Chemical constituents
Quantity in gram
Quantity in %
1
2
3
4
5
Na+
K+
ClNO3PO43-
0.234
3.993
4.012
0.013
0.053
2.75
46.96
47.19
0.15
0.62
The product consists of considerably very high percentage of K+(46.96%) and
Cl-(47.19%) as compared to other constituents (Table V.1 & Table V.2). On the other
hand, a very small quantity of the total mass consists of NO3- (0.15%) and PO43(0.62%). It is interesting to note that 89.71% of the total mass of the solid consists of
potassium chloride (KCl) and 7.00% of sodium chloride (NaCl). Other 3.29% consists
of Cl-, NO3-, PO43- and trace metals such as Al, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb,V
and Zn. These trace metals are essential minerals, play a vital role in our body function.
They act as co-factors for enzyme reaction, maintain pH within the body, maintain
proper nerve conduction, help to contract and relax muscles, help to regulate our body’s
tissue growth, provide structural and functional support for the body etc.25 Moreover
little sodium and high potassium makes the solid useful for human health by reducing
the risk of high blood pressure and cardiovascular disease associated with a high intake
of sodium chloride.26 It is cheap and natural. Assamese people are traditionally
132
usingkolakhar as an additive to food items. Due to these benefits, the solid obtained
from leaf sheath of banana plant (Musa balbisiana) pseudo-stem fibre may become the
best salt alternatives.
TableV.2:Composition of trace metals in the white crystalline product
Entry
Metal
mg/100g
1
Al
50.841
2
Cd
0.029
3
Co
0.253
4
Cr
0.129
5
Cu
0.488
6
Fe
38.447
7
Mg
3.424
8
Mn
0.312
9
Ni
4.712
10
Pb
0.035
11
V
2.053
12
Zn
3.129
The Food and Nutrition Board, The Institute of Medicine, National Academies
has recommended the adequate intakes for individuals of age group 31-70 year, as Cr is
0.02 -0.035 mg/d, Cu is 0.90 mg/d, Fe is 8 mg/d (18 mg/d for female of age group 3150 year), Mg is 320-420 mg/d, Mn is 1.8-2.3 mg/d, Zn is 8-11 mg/d, and P is 700
mg/d.27On the other hand, the adequate intake level of Al for adult is 5-150 mg/d28
whereas the provisional tolerable weekly intake (PTWI) for Cd and Pb are 0.007 mg/ kg
body weight and 0.025 mg/kg body weight29 respectively. Tolerable upper intake level
of Ni and V are 1.0 mg/d and 1.8 mg/d30for adults. The adequate intake level for Co is
0.01-0.02 mg/d for both the male and female adults31 but safe upper limit is 1.4 mg/d
and in case of Cr, the safe upper limit is 10 mg/d.32
Modern civilization has changed the food habits of mankind. Owing to more
intake of salty and spicy readymade food, scientists have become aware of the health
risks associated with high salt (NaCl) intake, and limited to 1500–2300 mg of sodium
133
per day and potassium 4700 mg /day which is more than twice of sodium.
The recommended daily allowance of potassium is higher than that for sodium,33 yet a
typical person consumes less potassium than sodium in a given day.34 A person who
takes relatively high dietary potassium haslower blood pressure than who take relatively
low potassium.35 The Third National Health and Nutrition Examination Survey
(NHANES III) indicated that higher dietary potassium intakes were associated with
significantly lower blood pressures.36In 2004, the Food and Nutrition Board of the
Institute of Medicine established an adequate intake level for potassium based on
different age group that have been found to lower blood pressure, reduce salt sensitivity,
and minimize the risk of kidney stones37(Table V.3).
Table V.3: Adequate intake levels of potassium with different age groups
Adequate Intake (AI) for Potassium
Infants
0-6 months
Males
(mg/day)
400
Infants
7-12 months
700
700
Children
1-3 years
3,000
3,000
Children
4-8 years
3,800
3,800
Children
9-13 years
4,500
4,500
Adolescents
14-18 years
4,700
4,700
Adults
19 years and older
4,700
4,700
Pregnancy
14-50 years
-
4,700
Breast-feeding
14-50 years
-
5,100
Life Stage
Age groups
Females
(mg/day)
400
Table V.4: Quantity of major constituents in 1st and 2nd crops after fractional
crystallization
Total
weight
(g)
Na+
K+
Cl-
NO3-
PO43-
Quantity of constituents (in gram)
Total mass
accounted for
(g)
%
Entry
Sample
code
1
1stcrop
8.1142
0.0369
4.0950
3.8028
BDL
0.017
7.9517
97.99
2
2ndcrop
8.8910
0.4311
3.8910
4.1762
0.023
0.088
8.6093
96.83
134
The white crystalline product, on careful fractionation, yields two fractions, 1st
crop and 2nd crop. Analyses show that the 1st crop consists of nearly 97% of K+ and Clwhile the 2nd crop consists of about 90% of K+ and Cl-(Table V.4& Table V.5). Na+ in
1st crop is only about 0.45% against 4.85% in the 2nd crop. While NO3- content was not
detected in the 1st crop, it was present in the 2nd crop to the extent of 0.26%. Presence of
PO43- in the 1st crop is also much lower (0.21%) as compared to that in the 2nd crop
(0.99%). Thus 1st crop consists of higher percentage of KCl and lower impurities as
compared to 2nd crop (Table V.5).
Table V.5: Percentage (w/w) of major constituents in 1st and 2ndcrops after
fractional crystallization
Entry
1
2
3
4
5
Chemical
constituents
Na+
K+
ClNO3PO43-
Quantities in % in
1stcrop
0.45
50.48
46.87
BDL
0.21
Quantities in %
in 2ndcrop
4.85
43.76
46.97
0.26
0.99
The concentration of trace metals in 1st and 2ndcropswas estimated by Atomic
Absorption Spectrometric method and the results are tabulated in terms of ppm in the
solution and in mg/100g of the solid sample. Results show that major parts of the trace
Table V.6: Concentration of trace metals in ppm of 1stcrop (8.1142 g salt
wasdissolved in 500 ml distilled water) and in mg/100g in 1st fraction
Entry
1
2
3
4
5
6
7
8
9
10
11
12
Metal
Al
Cd
Co
Cr
Cu
Fe
Mg
Mn
Ni
Pb
V
Zn
ppm
1.302
BDL
0.126
BDL
BDL
0.982
0.078
BDL
0.097
0.041
0.074
0.064
135
mg/100g
16.046
1.553
12.102
0.961
1.195
0.058
0.912
0.789
Table V.7: Concentration of trace metals in ppm of 2ndcrop (8.8910 g salt
wasdissolved in 500 ml distilled water) and in mg/100g
Entry
1
2
3
4
5
6
7
8
9
10
11
12
Metal
Al
Cd
Co
Cr
Cu
Fe
Mg
Mn
Ni
Pb
V
Zn
ppm
7.341
0.029
0.617
0.081
0.076
5.550
0.504
0.046
0.704
BDL
0.276
0.468
mg/100g
82.576
0.326
6.940
0.091
0.855
62.423
5.669
0.517
7.918
3.104
5.264
metals appear in the 2nd crop (Table V.6 & Table V.7). For example there is 7.341 ppm
of Al in the 1st crop against 82.576 ppm in the 2nd crop. Similarly against 5.550 ppm of
Fe in the 1st crop, there is 62.423 ppm in the 2nd crop. Presence of other heavy metals
such as Cd, Co, Cr, Cu, Mn, Ni, V and Zn are also higher in the 2nd crop as compared to
those in 1st crop.
V.4 Conclusion
The water extract of banana pseudo-stem fibre ash (kolakhar from fibre) is a
strong alkali having pH 10.9 where potassium level is much higher as compared to that
of sodium level. Chloride content is much lower than that of carbonate level. After
neutralization by hydrochloric acid, it contains only chloride in place of carbonate. The
solid recovered after evaporation of the neutralized aqueous extract with HCl to
dryness, contains 89.71% potassium chloride and rest of the part contains Na+, Cl-, NO3, PO43- and trace metals Al, Fe, Cd, Co, Cu, Cr, Mg, Mn, Ni, Pb, V and Zn. The higher
level of potassium chloride enhances the quality to be used as an alternative to common
salt for the patients of high blood pressure.
The first croprecovered from the fractional crystallization of kolakar contains
96.41% potassium chloride and the rest contains Na+, Cl-, NO3-, PO43- and trace metals
136
Al, Fe, Cd, Co, Cu, Cr, Mg, Mn, Ni, V and Zn. This white crystalline solid is a better
substitute for common salt and could find other uses in pharmaceutical and industries.
The 2nd crop contains about 83.60% potassium chloride, and is less pure
potassium chloride as compared to the 1st crop and can be used as fertilizer, deicer,
water softener and industrial purposes. It may be a better potash fertilizer because it
contains not only potassium but also phosphorous and nitrogen which are plant essential
minerals
137
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