Biosorption of cesium(Ⅰ) from aqueous solution by a novel exopolymers secreted from Pseudomonas fluorescens C-2: Equilibrium and kinetic studies

The biosorption characteristics of Cs（I） ions from aqueous solution using exopolymers （PFC02） produced from Pseudomonas fluorescens C-2 were investigated as a function of pH, biosorbent dosage, contact time and initial concentration. pH played a major role in the adsorption process, and the optimum pH for the removal of Cs（I） was 8.0. Langmuir, Freundlich and Dubinin-Radushkevich （D-R） models were applied to describe the biosorption isotherm of the Cs（I） ions by PFC02. The Lagergren first-order, pseudo second-order kinetic and intraparticle diffusion models were used to test the kinetic data. Langmuir model and D-R model fitted the equilibrium data better than the Freundlich isotherm. The monolayer adsorption capacities of PFC02 as obtained from Langmuir isotherm at 25°C was found to be 32.63 mg/g. From the D-R isotherm model, the mean free energy was calculated as 26.73 kJ/mol, indicating that the biosorption of cesium was chemisorption. The biosorption process was rapid, and the kinetic rates were best fitted to the pseudo second-order model, which indicated the biosorption process operated through chemisorption mechanism. FT-IR analysis of PFC02 showed the possible functional groups responsible for cesium adsorption were hydroxyl, carboxyl, carbonyl and sulphonate groups. SEM analysis showed the porous structure of the material while EDX analysis confirmed the adsorption of Cs（I） on PFC02. Cesium adsorbed onto the PFC02 could be desorbed efficiently using 1 mol/L HNO 3 , and the enrichment factor was 50.0. Furthermore, PFC02 could be reused five times with only about 8.25% regeneration loss. The developed method was successfully utilized for the removal of Cs（I） ions from aqueous solution.

Valorisation of alum sludge to produce green and durable mortar

Alum sludge is a typical by-product of drinking water treatment processes.Most sludge is disposed of at landfill sites,and such a disposal method may cause significant environmental concern due to its vast amount.This paper assessed the feasibility of reusing sludge as a supplementary cementitious material,which could efficiently exhaust stockpiled sludge.Specifically,the pozzolanic reactivity of sludge at different temperatures,the reaction mechanism of the sludge-cement binder,and the resistance of sludge-derived mortar to microbially induced corrosion were investigated.The obtained results indicated that 800℃ was the optimal calcination temperature for sludge.Mortar containing sludge up to 30%by weight showed comparable physical properties at a curing age of 90 days.Mortar with 10%cement replaced by sludge can significantly improve the resistance to biogenic corrosion due to the formation of Al-bearing phases with high resistance to acidic media,e.g.,Ca_(4)Al_(2)O_(7)·xH_(2)O and strätlingite.