Papermaking sludge, rich in intrinsic resource value, is effectively barred from direct deployment in environmental remediation, agriculture, or energy generation by its pronounced contaminant burden. Pyrolytic conversion into high-value paper sludge biochar, such as papermaking sludge biochar (PSBC) provides a green, efficient portal for closing its resource loop. In this study, papermaking sludge was converted into a series of paper sludge biochars (PSBCs) via oxygen-limited pyrolysis at 500–900 °C. The porous architecture, surface physicochemical properties, and crystalline structure of the biochars were comprehensively characterized, and their performance for aqueous tetracycline (TC) removal was systematically quantified. Pyrolysis at 900 °C afforded PSBC 900 with the lowest yield (36.05%) yet the highest Brunauer–Emmett–Teller (BET) surface area (79.53 m2/g), an extensively developed mesopore network, and the greatest degree of graphitization. Across an initial tetracycline (TC) concentration window of 20–160 mg/L, PSBC 900 delivered an equilibrium capacity (qe) of 72.22 mg/g, outperforming PSBC 700 and PSBC 500 by factors of 1.3 and 1.8, respectively. Optimal uptake was achieved at a dosage of 1.0 g/L, pH 7, and 120 min contact time. Among the background cations examined, Mg2+ exerted a pronounced inhibitory effect, whereas Na+, K+, and Ca2+ exerted negligible interference. The adsorption process was accurately described by the pseudo-second-order kinetic model and the Langmuir isotherm (R2 > 0.999), yielding a theoretical maximum capacity (qm) of 76.39 mg/g for PSBC 900 at 313 K. Thermodynamic parameters (∆Gθ 0, ∆Sθ > 0) confirm a spontaneous, endothermic, and entropy-driven process. After five consecutive adsorption–desorption cycles, PSBC 900 retained >64.68% of its original efficiency, demonstrating excellent regenerability. Paper sludge biochar enables a “waste-to-treat-waste” strategy for the efficient abatement of tetracycline, offering an economically viable and high-performance technology that advances the remediation of tetracycline-laden wastewaters.
Jiayu Niu (Thu,) studied this question.