Cr(Ⅲ) adsorption by sugarcane pulp residue and biochar

A batch experiment was conducted to investigate the adsorption of trivalent chromium （Cr（Ⅲ）） from aqueous solutions by sugarcane pulp residue （SPR） and biochar. The results show that Cr（Ⅲ） adsorption by SPR and biochar is highly pH-dependent and Cr（Ⅲ） adsorption amount increases with the increase of pH. The adsorption kinetics of Cr（Ⅲ） fits well with the pseudo-second-order model. The maximum Cr（Ⅲ） adsorption capacities of 15.85 mg/g and 3.43 mg/g for biochar and SPR were calculated by Langmuir model. This indicates that biochar has a larger ability for Cr（Ⅲ） adsorption than SPR. The free energy change value （AG） reveals a spontaneous sorption process of Cr（Ⅲ） onto SPR and non-spontaneous sorption process onto biochar. The entropy change （AS） and enthalpy change （AH） are found to be 66.27 J/（mol＇K） and 17.13 kJ/mol for SPR and 91.59 J/（mol-K） and 30.875 kJ/mol for biochar which further reflect an affinity of Cr（Ⅲ） onto SPR and biochar. It is suggested that biochar has potential to be an efficient adsorbent in the removal of Cr（Ⅲ） from industrial wastewater.

Removal of Cr(Ⅲ) and Cr(Ⅵ) from aqueous solution by adsorption on sugarcane pulp residue

Sugarcane pulp residue （SPR）, a waste from sugar-refinery, which possesses a large surface area, can be used for removing chromium （Cr（Ⅲ） and Cr（Ⅵ）） from wastewater. In this work, the kinetics, isotherms of Cr（Ⅲ） and Cr（V[） adsorption and their removal by SPR were investigated. The results show that the removal percentages of Cr（Ⅵ） and Cr（Ⅲ） increase with increasing SPR dosage and temperature and decrease with increasing SPR particle size and the initial concentration of chromium ions. However, the influence of pH value on the Cr（Ⅵ） removal differs from that of the Cr（Ⅲ） removal. The Cr（Ⅵ） removal percentage decreases with increasing pH values, while the Cr（Ⅲ） removal percentage increases with increasing pH value. The adsorption kinetics of Cr（Ⅵ） and Cr（Ⅲ） well fits with pseudo-second-order model. Langmuir adsorption isotherm can well describe the adsorption phenomena of chromium ions with the maximum adsorption capacity of 0.567 mg/g for Cr（Ⅵ） and 3.446 mg/g for Cr（Ⅲ）. Moreover, SPR reveals higher adsorption capacity for Cr（Ⅲ） than that for Cr（Ⅵ）, which implies that SPR has more potential application for Cr（Ⅲ）-containing wastewater treatment than that for Cr（Ⅵ）-containing wastewater treatment.

Heterogeneous fenton oxidation of methylene blue with Fe-impregnated biochar catalyst

Fe-impregnated biochar(Fe-BC)as high-efficiency heterogeneous Fenton catalyst was synthesized and evaluated in detail for its catalytic activity,stability and reusability under various conditions.The optimal conditions for the Fenton oxidation of methylene blue(MB)as model dye were determined as 0.075 g/L H_(2)O_(2),0.5 g/L Fe-BC for 0.1 g/L MB,which resulted in optimum Dye:Fe_(cat):H_(2)O_(2) ratio of 1:5:0.75(on g/L basis)or[Dye]:[Fe_(total)]:[H_(2)O_(2)]molar ratio of 1:6.2:7.0 respectively.The effective degradation of MB was identified over a wider pH range,and even after four consecutive runs Fe-BC maintained above 95%MB removal rate within 3 min of treatment with low Fe release,indicating strong stability and reusability.Under the optimum Dye:Fe_(cat):H_(2)O_(2)(g/L)condition at initial pH 4,the Fe-BC achieved 99.9%removal efficiency of MB within 3 min in heterogeneous Fenton reaction(HEFR)with much less H_(2)O_(2) concentration and low catalyst dosage,demonstrat-ing its efficiency and cost-effectiveness compared to other Fenton reaction catalysts.The removal velocity of MB showed two rate steps:a fast first stage followed by a slow stage with the rate in the order of H_(2)O_(2)/Fe-BC⋙H_(2)O_(2)/biochar>biochar>H_(2)O_(2).Overall,the developed Fe-BC is more economical with strong stability and recyclability for use in HEFR for treating recalcitrant pollutants.