This study developed an adsorbent for cobalt(II) ions, in the form of nanomagnetite coated with carboxymethyl kappa-carrageenan cross-linked Bisphenol A Diglycidyl Ether (BADGE) with a magnetite solid phase extraction technique (Magnetic Solid Phase Extraction, MSPE). This adsorbent consists of nanomagnetite as a core and a functional layer on its surface. The purpose of this study was to synthesize nanomagnetite coated with carboxymethyl kappa-carrageenan (CMKC) crosslinked with BADGE, as an adsorbent of Co(II) ions and to test its ability in repeated use. The stages of this research are, the first stage is the synthesis of nanomagnetite and its characterization using SEM, FTIR, and XRD instruments, the second stage is the synthesis of CMKC and its characterization using the FTIR instrument, the third stage is the synthesis of crosslinked CMKC coated nanomagnetite BADGE, The synthesis results were characterized using FTIR and SEM instruments. The fourth stage of the adsorbent was tested for its adsorption ability on water samples containing Co(II) ions. The CMKC coated nanomagnetite crosslinked with BADGE which has been successfully synthesized has a rough, porous, and pleated adsorbent surface. The FTIR spectrum of the adsorbent showed a shift in the C=O asymmetric vibration peak from 1634 cm-1 to 1646 cm-1 after crosslinking. The adsorption ability test of BADGE cross-linked CMKC-coated nanomagnetite adsorbent on water samples containing Co(II) ions showed an adsorption capacity of 3.1 mg Co(II)/gram adsorbent. The repeated use of the cross-linked CMKC coated nanomagnetite adsorbent decreased the adsorption capacity by 24% from the adsorption capacity in the first use, which was 86%.
