Porous Spherical Granulation of Co-Doped Manganese-Based Lithium Ion-Sieve with Solid Paraffin as Mesoporous Porogen for Lithium Recovery from Salt Lake Brine

Manganese-based lithium ion-sieves (LIS) are promising adsorbents for lithium extraction from salt lake brines. Their powder form, however, hinders industrial application because it disperses poorly, is difficult to recover, and causes excessive pressure drop in fixed-bed columns. Here we address this powder-forming challenge through porous spherical granulation, using solid paraffin as a mesoporous porogen. Co-doped precursors were prepared by hydrothermal-calcination. XPS showed that Co doping raised the Mn⁴⁺ ratio from 65.77% to 72.16%, which suppresses the Jahn-Teller effect. The optimal powder reached 33.36 mg/g in LiCl solution and retained 89.0% of this capacity after five cycles. For granulation, the powder was modified with octadecyltrimethoxysilane (OTMS) and granulated by suspension polymerization. The solid paraffin porogen created mesoporous channels that increased the BET surface area from 0.82 to 82.00 m2/g. The optimized granule reached 4.42 mg/g in LiCl solution and 1.56 mg/g in real salt lake brine, with separation factors of 357.0, 256.5, 225.4, and 41.87 for Na⁺, K⁺, Mg²⁺, and Ca²⁺, respectively. It kept 62% of its capacity after 20 cycles, and Mn dissolution stabilized at 0.18%. The combined doping and pore-engineering strategy offers a viable route to lithium extraction from salt lake brines.