4.5 Extraction of Alginates
75
softened by soaking in 0.2 M HCL overnight. An alkali, sodium carbonate is then
added under high temperature (~80 °C) to extract sodium alginate in an aqueous
mixture with the seaweed residue. The solid residue is then separated by filtering
(Fertah et al. 2017). The process then proceeds using either of the two methods below
to recover the sodium alginate from the aqueous solution.
4.5.2 Method 1
The first method involves the addition of calcium salt to the liquid extract which
results in the formation of calcium alginate which is insoluble in water. This can
therefore be separated from the mixture by filtration or pressing. This is followed
by adding acid to form alginic acid. Alcohol is also added to render the sodium
alginate to be formed, insoluble. Sodium alginate is then formed by the addition of
sodium carbonate which precipitates and is separated and dried followed by further
processing depending on the end use.
4.5.3 Method 2
In this method, acid is first added to the liquid extract. This results in the formation
of alginic acid. This alginic acid is insoluble in water forming a soft gel which can
be separated from the aqueous mass. This is followed by addition of alcohol and
then an alkali, sodium carbonate to form sodium alginate from the alginic acid. The
alcohol added to the water allows the sodium alginate to precipitate out of the water
once formed, thus making it easier to separate. The product, sodium alginate can
then be dried and used for further processing and application. This method makes
use of mainly acid and alcohol.
4.5.4 Method 3
In this method following the sodium carbonate extraction, the sodium alginate is
precipitated using ethanol (Fertah et al. 2017). This method is more commonly used
for laboratory-scale extraction where dewatering processes might be impractical at
the small scale and alginate of high purity is required. Furthermore, this method can
be used where cost saving is not of concern, and the alginate is being extracted,
mainly for research purposes.
All these methods generally involve the addition of acid to dissolve the sodium
alginate from the seaweed mass. This alkaline extraction takes about two hours and
requires a hot solution of sodium carbonate. The seaweed residue is then separated
from the liquid. The main task that follows is therefore to separate the sodium alginate
75
softened by soaking in 0.2 M HCL overnight. An alkali, sodium carbonate is then
added under high temperature (~80 °C) to extract sodium alginate in an aqueous
mixture with the seaweed residue. The solid residue is then separated by filtering
(Fertah et al. 2017). The process then proceeds using either of the two methods below
to recover the sodium alginate from the aqueous solution.
4.5.2 Method 1
The first method involves the addition of calcium salt to the liquid extract which
results in the formation of calcium alginate which is insoluble in water. This can
therefore be separated from the mixture by filtration or pressing. This is followed
by adding acid to form alginic acid. Alcohol is also added to render the sodium
alginate to be formed, insoluble. Sodium alginate is then formed by the addition of
sodium carbonate which precipitates and is separated and dried followed by further
processing depending on the end use.
4.5.3 Method 2
In this method, acid is first added to the liquid extract. This results in the formation
of alginic acid. This alginic acid is insoluble in water forming a soft gel which can
be separated from the aqueous mass. This is followed by addition of alcohol and
then an alkali, sodium carbonate to form sodium alginate from the alginic acid. The
alcohol added to the water allows the sodium alginate to precipitate out of the water
once formed, thus making it easier to separate. The product, sodium alginate can
then be dried and used for further processing and application. This method makes
use of mainly acid and alcohol.
4.5.4 Method 3
In this method following the sodium carbonate extraction, the sodium alginate is
precipitated using ethanol (Fertah et al. 2017). This method is more commonly used
for laboratory-scale extraction where dewatering processes might be impractical at
the small scale and alginate of high purity is required. Furthermore, this method can
be used where cost saving is not of concern, and the alginate is being extracted,
mainly for research purposes.
All these methods generally involve the addition of acid to dissolve the sodium
alginate from the seaweed mass. This alkaline extraction takes about two hours and
requires a hot solution of sodium carbonate. The seaweed residue is then separated
from the liquid. The main task that follows is therefore to separate the sodium alginate