Magnesium nitrate hexahydrate
(Mg(NO3)2·6H2O, 98%), zinc nitrate
hexahydrate (Zn(NO3)2·6H2O,
98%), aluminum nitrate nonahydrate (Al(NO3)3·9H2O, 98%), hydrochloric acid (HCl), calcium sulfate
(CaSO4·2H2O), and potassium nitrate (KNO3) were obtained from Sigma-Aldrich (South Africa). Sodium
hydroxide (NaOH), acetic acid (CH3COOH), calcium nitrate
(Ca (NO3)2·6H2O), and sodium
nitrate (NaNO3) were obtained from Minema Chemicals (South
Africa). Sodium alginate was obtained from SRL (Sisco Research Laboratories,
India). Ultrapure water obtained by a Milli-Q system (Merck Millipore,
Merck, South Africa) was used in all experimental methods.