Demineralization of Silica-Rich Agar Processing Residues via Hydrofluoric Acid Leaching for Organic Fraction Enrichment

Andi Sudarma; Edy Hartulistiyoso; Yohanes Aris Purwanto; Leopold Oscar Nelwan; Obie Farobie; Hendri Hendri; Harri Junaedi; Edy Herianto Majlan

doi:10.22441/ijimeam.v8i2.38546

Authors

Andi Sudarma IPB University, Indonesia http://orcid.org/0000-0002-8825-9193
Edy Hartulistiyoso IPB University, Indonesia http://orcid.org/0000-0002-5837-1555
Yohanes Aris Purwanto IPB University, Indonesia http://orcid.org/0000-0002-2547-0717
Leopold Oscar Nelwan IPB University, Indonesia http://orcid.org/0000-0001-7907-3285
Obie Farobie IPB University, Indonesia http://orcid.org/0000-0002-6159-635X
Hendri Hendri Institut Teknologi PLN, Indonesia http://orcid.org/0009-0005-4702-1786
Harri Junaedi Prince Sultan University, Saudi Arabia
Edy Herianto Majlan Universiti Kebangsaan Malaysia, Malaysia http://orcid.org/0000-0001-9327-7153

DOI:

https://doi.org/10.22441/ijimeam.v8i2.38546

Keywords:

agar solid waste, hydrofluoric acid leaching, demineralization, silica removal, higher heating value

Abstract

Agar solid waste (ASW) is a silica-rich by-product generated during agar extraction and its utilization is limited by high inorganic content, high ash, and low energy value. This study investigates the demineralization of ASW using hydrofluoric acid (HF) to reduce the silica-rich mineral fraction and improve its biomass characteristics. ASW samples obtained from two agar-processing plants contained celite- and perlite-derived impurities, resulting in very high ash contents of up to 85.84 wt% and low higher heating values (HHV). HF leaching was conducted using 10 wt% HF for 45 min. The results showed that ash content decreased markedly to 24.83–44.99 wt%, confirming substantial mineral removal. ICP-MS and FTIR analyses further verified the reduction of silica-related species after treatment. Demineralization also caused a relative enrichment of the organic fraction, as reflected by the increase in carbon content up to 16.10 wt% and the more prominent appearance of organic functional groups in the FTIR spectra. As a consequence, the HHV improved significantly, particularly for ASW-A, increasing from 1.91 to 6.52 MJ/kg. Differences between ASW-A and ASW-B indicate that filtration aid type influences leaching efficiency and the resulting material properties. Overall, HF leaching proved effective for upgrading silica-rich ASW, enhancing its suitability for thermochemical conversion and supporting its valorization into higher-value biomass-derived products.

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