Dj. Mchugh et al., Pilot plant scale extraction of alginates from Macrocystis pyrifera - 3. Precipitation, bleaching and conversion of calcium alginate to alginic acid, J APPL PHYC, 13(6), 2001, pp. 471-479
Three steps of the alginate production process were studied at pilot plant
level. The effect of the amount of calcium chloride used during the precipi
tation was measured in terms of filtration time of the precipitated calcium
alginate. Three different proportions of calcium chloride per gram of algi
nate were tested. The best proportion used was 2.2 parts of calcium chlorid
e per one part of alginate, yielding a filtration rate of 97.9 L min(-1) on
a screen area of 1.32 m(2). The method of adding the solutions and the deg
ree of mixing are discussed as other factors affecting the precipitation st
ep. The effect of bleaching the calcium alginate with sodium hypochlorite (
5%) was studied. Seven proportions, ranging from 0 to 0.77 mL of sodium hyp
ochlorite per gram of sodium alginate were tested. The effect of hypochlori
te was compared for alginates with three different viscosities. Using algin
ates with medium viscosity (300-500 mPa s), the best proportion was 0.4 mL
hypochlorite per gram of alginate, yielding an alginate of light cream colo
r with 20% less viscosity than the control. Alginates with lower viscosity
showed a smaller loss of viscosity. The effect of pH during conversion of c
alcium alginate to alginic acid was determined using four combinations of p
H, ranging from 2.2 to 1.6, in three acid washings. The extent of conversio
n was determined by measuring the percent reduction of the alginate viscosi
ty (RV) in 1% solution before and after adding a sequestrant of calcium. Wh
en a pH 1.8 or 1.6 was used for each washing, only two washings were necess
ary to produce a RV lower than 40% (maximum recommended). The use of pH 2 r
equired three acid washings to produce the same effect. The pH 2.2 did not
remove enough calcium, even with three washings, the RV of the resulting so
dium alginate being greater that 40%. The results of these experiments prov
ide the information that producers need when deciding the best parameters t
o obtain a product with the desired characteristics.