Effect of thermal pretreatment on the extraction of potassium salt from alga Saccharina japonica

Abstract

Interests in conversion of macroalgae to bioenergy via thermal treatment, namely pyrolysis or combustion has increased due to their distinctive composition and high photosynthetic rates. The resulting char byproducts could serve as a trove of precious mineral resources. Thermal pretreatment was compared with direct extraction of potassium salts from alga Saccharina japonica using deionized water for use as food additive, agricultural or pharmaceutical applications. Biomass was pyrolysed with fixed bed reactor or combusted with muffle furnace at 300, 450, 600 °C, and extracted using deionized water in shaker at 150 rpm and 30 °C for 2 h. Overall potassium salts recovery efficiency from raw biomass (52.55 ± 2.79%) was relatively lower than from 450 °C chars from pyrolysis (75.30 ± 0.81%) and combustion (62.07 ± 0.56%). Extracts from pyrolysed char at 600 °C had highest purity of KCl which is most abundant mineral in all products. SEM-EDX and ICP-OES elemental analysis confirmed absence of heavy metals such as As, Cu, Cd and Pb in extracts. Ratios of organic to inorganic fractions in extracts from thermally pretreated samples were much lower (∼0.1) than that of raw biomass (8.42).