Kinetics and thermodynamics of cyanide removal by ZnO@NiO nanocrystals

ZnO,NiO and ZnO@NiO nanocrystals were successfully synthesized and characterized by FTIR,XRD and SEM methods.The average particles sizes of ZnO,NiO and ZnO@NiO were32,50and48nm,respectively.The nanocrystals were examined assensors for cyanide removal.The cyanide sensing test revealed that,compared with the pure ZnO,NiO,the ZnO@NiO nanocrystalsexhibited highly improved sensing performances.The ZnO@NiO nano crystals were found to have better capacity for iron cyanidethan sodium cyanide.The effects of significant parameters such as contact time,pH(2-12),nanocrystal dose(0.02-0.4g)andcyanide concentration(5-50mg/L)on the removal of cyanide by nanocrystals were explored.At an optimum pH<5,over90%removal of20mg/L cyanide was obtained for nanocrystal dose of0.2g after30min contact time for iron cyanide by ZnO@NiOnano crystals.Cyanide removal was followed by pseudo second order kinetic model for ZnO@NiO nano crystals(k2=4.66×10-2andR2=0.999).The values of standard entralpy change of7.87kJ/mol and standard free energy change of-18.62kJ/mol at298K suggestthe adsorption of cyanide on nanocrystals is an endothermic and spontaneous process.ZnO@NiO nanocrystal is an efficient sensorfor removal of cyanide from water and wastewater.

Cyanide removal for ultrafine gold cyanide residues by chemical oxidation methods

Because of the highly toxic cyanide in the gold cyanide residues,cyanide must be removed for environmental protection.The process mineralogy of residues was studied firstly,and then cyanide removal was carried out by three chemical methods.The results showed that the residue mainly contained Si,S and Fe.Pyrite was the main metallic mineral,and the iron-complex cyanides make cyanide removal difficult.The minerals in residues were in ultrafine particle size with high monomer dissociation degrees.In H_(2)O_(2)oxidation process,the self-decomposition and side reactions resulted in high consumption of H_(2)O_(2).In Na_(2)S_(2)O_(5)-air oxidation process,the time for complete process was long because of the reactions between Na_(2)S_(2)O_(5)and O_(2).Na_(2)SO_(3)oxidation method was found to be a new method for cyanide removal without air inflation device.The cyanide content was reduced to the national standard level in 90 min at pH 9.0 with optimum Na_(2)SO_(3)dose of 2.0 g/L.

Removal of total cyanide in coking wastewater during a coagulation process: Significance of organic polymers

Whether a cationic organic polymer can remove more total cyanide （TCN） than a non-ionic organic polymer during the same flocculation system has not been reported previously. In this study, the effects of organic polymers with different charge density on the removal mechanisms of TCN in coking wastewater are investigated by polyferric sulfate （PFS） with a cationic organic polymer （PFS-C） or a non-ionic polymer （PFS-N）. The coagulation experiments results show that residual concentrations of TCN （Fe（CN）6^3-） after PFS-C flocculation （TCN 〈 0.2 mg/L） are much lower than that after PFS-N precipitation. This can be attributed to the different TCN removal mechanisms of the individual organic polymers. To investigate the roles of organic polymers, physical and structural characteristics of the floes are analyzed by FT-IR, XPS, TEM and XRD. Owing to the presence of N＋ in PFS-C, Fe（CN）3- and negative flocs （Fe（CN）63- adsorbed on ferric hydroxides） can be removed via charge neutralization and electrostatic patch flocculation by the cationic organic polymer. However, non-ionic N in PFS-N barely reacts with cyanides through sweeping or bridging, which indicates that the non-ionic polymer has little influence on TCN removal.

Through converting the surface complex on TiO_(2) nanorods to generate superoxide and singlet oxygen to remove CN^(−)

Cyanide(CN−)is extensively used in the process of plating devices and for surface treatment in the electroplating industry and is extremely hazardous to humans and the environment.Peroxymonosulfate(PMS)-based advanced oxidation processes(AOPs)hold considerable promise for CN−removal.However,the activity of sulfate radical and hydroxyl radical generated in the PMS activation process is low in the base condition,leading to a drop in its efficiency in CN−removal.Thus,a photo-electrocatalytic system(PEC),developed using a TiO_(2) photoanode and a carbon aerogel cathode,was used to activate PMS for the removal of CN−from wastewater through the generation of radicals and non-radicals.The PEC/PMS system could effectively remove CN^(−),with the removal efficiency reaching 98.5%within 2 min,when PMS concentration was at the 0.25 mmol/L level,and the applied bias voltage was-0.5 V.The main active species in the PEC/PMS system were superoxide radicals and singlet oxygen,which was proved through electron paramagnetic resonance detection and quenching experiments.Results obtained through in-situ Raman measurements,photocurrent tests,and electrochemical impedance spectroscopy measurements indicated that the TiO2 could activate PMS to generate active species.Following many cycles of experimentation,it was discovered that the system displayed high catalytic performance and possessed satisfactory stability to remove CN−economically and efficiently.