Search

This study addresses the preparation of sludge biochar through a procedure that combines steam pyrolysis in a wide range of temperature (500–900 ºC) and acid treatment with HCl (performed before or after the pyrolysis). The acid washing after the pyrolysis maximizes BET surface area due to pore unblocking, thus making visible the pore structure generated. The drawback of the acid washing is the lower yield obtained (compared to the acid pretreatment), as well as the loss of the magnetic properties of sludge biochar. The acid pretreatment requires temperatures above 700 ºC to have a beneficial effect, due to the occurrence of additional reactions of the incorporated HCl with sludge constituents. The pretreatment results in materials with a high degree of microporosity. Among the reactions favoured, of interest is the development of magnetite in the whole temperature range. The activation protocol used in this study (especially the procedure that includes the acid pretreatment) is effective to generate biochar with magnetic properties through the transformation of the Fe introduced during the water treatment process, without adding a source of Fe. The presence of magnetite is an advantage for the reuse of sludge biochars in wastewater treatment. • Acid washing after steam activation greatly enhances porosity due to pore unblocking. • Acid pretreatment produces biochars with a high degree of microporosity. • Acid pretreatment leads to the formation of magnetite in the whole temperature range. • The acid treatment results in the generation of C=O, -OH and -NH functionalities. • The activation protocol is effective to produce magnetic biochar without adding Fe. [ABSTRACT FROM AUTHOR]

A porous biochar was manufactured through the valorization of waste pork bones, following a three-step process including pre-charring under mild conditions, acid treatment and thermal activation. The influence of the acid (H2SO4 and H3PO4) and the impregnation ratio on the physicochemical properties of the material was investigated. Acid treatment at 0.2 mmolacid/gprecursor increased BET area by about 80%, compared to untreated bone char. When using H2SO4, higher impregnation ratios significantly enhanced microporosity (up to 263%). This increased microporosity should be associated to a specific reaction mechanism of H2SO4 with a source of carbon. On the contrary, the higher activity of H3P04 led to a dramatic removal of porosity for large impregnation ratios (about 20mmol/g). The acid activation mechanism involves the formation of cation-deficient HAp, which is thereafter decomposed upon thermal treatment. The maximum uptake of methylene blue was achieved at low impregnation ratios (0.2 and 1.0mmol/g), and could be related to surface area corresponding to large micropores and small mesopores. [ABSTRACT FROM AUTHOR]

Microporous biochars, mainly composed by hydroxyapatite (HAp), were prepared from animal waste bones. In this study, a three-step procedure including pre-pyrolysis, chemical treatment with NaOH, KOH and KCO, and pyrolysis was investigated. The effects of the activation agent and its concentration were analysed by N adsorption-desorption, SEM, EDX, FTIR, and XRD techniques. The activation mechanism was investigated by TG-MS. FTIR and XRD data confirm that the obtained biochars were mainly composed of HAp. KCO was the most effective with porosity being increased by 30 % (up to 234 m/g) compared to non-alkali-treated sample. New pores were generated mainly in the microporous range. Analysis of the pyrolysis gases by MS revealed that the main effect of the alkali treatment is the incorporation of OH ions, which then react with bone matrix to generate porosity. Other gas-phase reactions, such as reverse WGS and methanation reactions, promoted by KCO, may be involved in the activation process. In contrast, KOH caused little modification of the HAp structure. Statistical analysis supported the relationship among the release of certain compounds during pyrolysis and the textural properties of the final material. [ABSTRACT FROM AUTHOR]