ADSORPTION OF Pb2+ IONS BY HEMP HURD BIOCHAR FROM INDUSTRIAL HEMP (CANNABIS SATIVA)

Abstract

The adsorption properties of three sor­bent forms derived from industrial hemp hurd (Cannabis sativa L., ‘Glianytsia’ variety, Poltava region, Ukraine) untreated (US), partially carbonized at 350 °C for 45 min (PC) and fully carbonized biochar at 550 °C for 75 min (BC) were studied for Pb²⁺ removal from model aqueous solutions. Equilibrium data were described by the Langmuir and Freundlich mo­dels with parameters determined by nonlinear least-squares regression (SigmaPlot 15.0).  The Langmuir model provided a physically sound description due to its saturation plateau corresponding to the finite number of active sites; the maximum sorption capacity q_max increa­sed as US (103.1 mg/g) < PC (177.3 mg/g) < BC (247.1 mg/g), approaching commercial activated carbon (200−350 mg/g). Although the Freundlich model yielded comparable R² va­lues, it overestimated q_e at high equilibrium concentrations, confirming the Langmuir pre­fe­rence on the basis of physical adequacy. Sorption kinetics followed the Ho–McKay pseudo-­second-order model (R² = 0.993−0.999), confirming chemisorption as the rate-limiting step. The initial sorption rate h₀ increased 5.7-fold from US (8.47 mg · g⁻¹ · min⁻¹) to  BC (47.98 mg · g⁻¹ · min⁻¹). Weber-Morris ana­lysis revealed two linear segments with non-zero intercepts, indicating combined contributions of external mass transfer and pore diffusion. Optimum pH was 5.0-6.0; BC showed the highest resistance to Ca²⁺/Mg²⁺ competition (capacity loss only 8−10 %). Regeneration with 0.1 M HNO₃ retained 90 % of BC capacity after five sorption-desorption cycles. The estimated production cost is 8−17 times lower than commercial activated carbon, making hemp hurd biochar an economically attractive alternative for Pb²⁺ removal from industrial wastewater.