Through converting the surface complex on TiO2 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 TiO2 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.

Cyanide removal from aqueous environment by resting cells and PTFE immobilized cells of Sphingobacterium spp.

Microbial detoxification of cyanide offered an inexpensive, safe, and viable alternative to physiochemical processes for the treatment of cyanide in industrial effluents or contaminated sites. This study involved isolation of novel strain with high resistance against cyanide toxicity and able to degrade the cyanide radical. The strain was isolated from rocky area and identified as Sphingobacterium multivorium using 16S ribosomal RNA. Resting pregrown cells were used in simple reaction mixture to avoid the complication associated with the media. One-gram fresh weight of this bacteria was able to remove 98.5% from 1.5 g/L cyanide which is a unique result. Factor affecting the biochemical process such as pH, temperature, agitation, glucose concentration was examined. The optimum conditions were, pH 6-7, 30-40°C, and 100-150 rpm shaking speed and 0.25% glucose. Furthermore, the cells were used after immobilization in polytetrafluoroethylene (PTFE) polymer. The PTFE is very safe carrier and the cells withstand the entrapment process and were able to remove 92% (1 g/L cyanide). The immobilized cells were used for six successive cycles with about 50% removal efficiency. The storage life extended to 14 days. No previous work studied the cyanide removal by Sphingobacterium spp. The strain showed good applicable characters.

Isolation and removal of cyanide from tailing dams in gold processing plant using natural bitumen.

Gilsonite as a natural occurrence of bitumen and due to the presence of carbon in its structure is a suitable adsorbent for a wide variety of pollutants. In this research, the adsorption of cyanide from the wastewater of gold processing plants using gilsonite were investigated. In this way, the effect of particle size of gilsonite, the weight and mixing time with solution, on the amount of cyanide adsorption have been studied. In addition, in one experiment, the effect of processed gilsonite on its adsorption ability was investigated. Based on the obtained results, the maximum adsorption of 61.64% was obtained in the size range of -1+0.5 and -2+1 mm of gilsonite. With increasing adsorbent weight and mixing time, the cyanide adsorption rate were increased. On the other hand, with the processing of the gilsonite sample, the amounts of adsorption were increased considerably. This study indicated that gilsonite can be used as an isolation and absorbent in the structure and floor of the tailing dumps of mineral processing plants.

Removal of cyanide adsorbed on pyrite by H2O2 oxidation under alkaline conditions.

Large amounts of cyanide tailings are produced during the cyanidation process in gold extraction, which are hazardous solid wastes due to the toxic cyanide. Pyrite is one of the main minerals in cyanide tailings. The removal of cyanide adsorbed on pyrite by H2O2 oxidation under alkaline conditions was investigated in this study. It was found that the removal efficiency was positively correlated with pH from 5 to 12, but remained almost constant when pH was higher than 12. The highest cyanide removal efficiency of 91.10% was achieved by adding no less than 0.6 wt.% of H2O2. Cyanide removal was positively correlated with the CN- adsorption amount between 1.06 and 8.5 mg/g, and temperature between 25 and 85°C. The removal of cyanide adsorbed on pyrite by H2O2 oxidation under alkaline conditions was due to the oxidation of pyrite. Hexacyanoferrate, thiocyanate and sulfate were generated with mole ratios of about 2.03:1.12:3.17 during the cyanide removal.

Interaction between Diethyldithiocarbamate and Cu(II) on Gold in Non-Cyanide Wastewater.

A surface-enhanced Raman scattering (SERS) detection method for environmental copper ions (Cu2+) was developed according to the vibrational spectral change of diethyldithiocarbamate (DDTC) on gold nanoparticles (AuNPs). The ultraviolet-visible (UV-Vis) absorption spectra indicated that DDTC formed a complex with Cu2+, showing a prominent peak at ~450 nm. We found Raman spectral changes in DDTC from ~1490 cm-1 to ~1504 cm-1 on AuNPs at a high concentration of Cu2+ above 1 µM. The other ions of Zn2+, Pb2+, Ni2+, NH4⁺, Mn2+, Mg2+, K⁺, Hg2+, Fe2+, Fe3+, Cr3+, Co2+, Cd2+, and Ca2+ did not produce such spectral changes, even after they reacted with DDTC. The electroplating industrial wastewater samples were tested under the interference of highly concentrated ions of Fe3+, Ni2+, and Zn2+. The Raman spectroscopy-based quantification of Cu2+ ions was able to be achieved for the wastewater after treatment with alkaline chlorination, whereas the cyanide-containing water did not show any spectral changes, due to the complexation of the cyanide with the Cu2+ ions. A micromolar range detection limit of Cu2+ ions could be achieved by analyzing the Raman spectra of DDTC in the cyanide-removed water.

Cyanide removal of gold cyanide residues by manganese compounds as new decyanation reagents.

Plenty of the toxic gold cyanide residues are produced by cyanidation process of gold extraction. As a kind of hazardous solid wastes, cyanide residues must be treated to remove cyanide before disposal. In this study, the removal of cyanide in gold cyanide residues by manganese compounds (KMnO4 and MnO2) was investigated. It was found that both KMnO4 and MnO2 could be used as new decyanation reagents for cyanide removal. To make the residue after cyanide removal meet the national standard, it needed KMnO4 1.8 wt% for 60 min reaction or MnO2 1.0 wt% for 30 min reaction with about pH 8.0. The mechanisms of two processes were investigated by X-ray photoelectron spectroscopy (XPS). The results show that KMnO4 concentrates on the reactions with pyrite in the cyanide residue, the products are mainly Fe(II), Fe(III), SO42- and MnO2. KMnO4 added in the slurry could be consumed by pyrite before oxidation of cyanide, resulting in relatively low cyanide remove efficiency and high KMnO4 consumption. On the surface of the residue after MnO2 treatment, there are mainly pyrite, Fe(II), Mn(II), Fe-CN and CN-, showing that the MnO2 process focuses on the removal of cyanide in the cyanide residue. The MnO2 process has the advantages of low reagents consumption, short reaction time and high cyanide removal efficiency, presenting a promise use for cyanide removal of cyanide residues in a range of applications.

Application of the anion-exchange resin as a complementary technique to remove residual cyanide complexes in industrial plating wastewater after conventional treatment.

Cyanide is highly toxic and must be destroyed or removed before discharge into the environment. This study examined the ability of commercial anion-exchange resins to remove residual cyanide complexes from industrial plating wastewater as a complement to conventional treatment. Cyanide removal experiments were conducted with various initial concentrations, reaction times, and temperatures, and the presence of co-existing anions. The maximum cyanide removal capacity (Qm) of the Bonlite BAMB140 resin is 31.82 mg/g and effectively removes cyanide from aqueous solution within 30 min. The cyanide removal by the resin is an endothermic process and is affected by the presence of anions in industrial plating wastewater. The relative competitiveness observed in this study was sulfate > nitrate > chloride. A mixture of 0.05 M NaCl and NaOH regenerates resin for continuous reuse for 5 cycles. The Bonlite BAMB140 resin was able to remove residual cyanide complexes from industrial plating wastewater, but the removal capacity of the resin was reduced by more than three times in batch (9.94 mg/g) and column (6349.12 mg/L) systems. Based on the results, the anion-exchange resins are expected to be used as a complementary technique to remove residual cyanide complexes in industrial plating wastewater after conventional treatment.

Synthesis of NiAl- layered double hydroxide with nitrate intercalation: Application in cyanide removal from steel industry effluent.

Cyanide contamination in steel plant wastewater is a challenge. Nitrate intercalated nickel aluminum layered double hydroxide (LDH) is specially designed and synthesized for adsorption of cyanide from wastewater. The LDH was characterized by Field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and BET surface analyzer. Formation of nanosized plate like LDH particles was confirmed by FESEM analysis. FTIR analysis confirmed the intercalation of nitrate ions in the interlayer space of nickel-aluminum layered double hydroxide. Adsorption of cyanide in the LDH matrix was identified by FTIR study. Ion exchange was the prevalent mechanism of cyanide adsorption. The specific surface area of LDH was 142 m2/g with average pore size of 1.9 nm. The spent LDH could be regenerated using a chemical method and was reused up to five cycles. The efficiency of the LDH was evaluated using real life cyanide containing wastewater from steel plant.

Novel cyanide electro-biodegradation using Bacillus pumilus ATCC 7061 in aqueous solution.

BACKGROUND: Electro-biodegradation is a novel technique for cyanide degradation in aqueous solutions. Many physical, chemical, and biological methods have been developed and used to treat cyanide degradation. The biological methods are more environmentally-friendly and economically cost-effective when compared to other techniques, however, the process reaction time period is much longer and the efficiency is lower. METHODS: In this research, the bacterial strain, Bacillus pumilus ATCC 7061, was tested for the first time to introduce the Cyanide Electro-biodegradation technique. By using a direct current power supply, electrons were generated in an electro-biodegradation cell containing culture media at free cyanide concentrations of 100 to 500 mg/l, under alkaline conditions. RESULTS: Experimental tests showed that when electrons were added and bacteria were inoculated into the aqueous media containing 100, 200, 300, 400 and 500 mg/l of free cyanide, the cyanide degradation efficiency increased from 16.2, 21.6, 29.5, 38.7 and 44.5% to 98.6, 99.3, 99.7, 99.8 and 99.7%, in 36, 72, 137, 233 and 301 h, respectively. The results show that by adding electrons, the process reaction time decreases and cyanide degradation efficiency increases significantly. CONCLUSIONS: The results presented here demonstrate for the first time the importance and the significance of the electro-biodegradation technique in the efficient degradation and removal of cyanide present in aqueous solutions.

Highly efficient one-step advanced treatment of biologically pretreated coking wastewater by an integration of coagulation and adsorption process.

A novel integrated process of coagulation and adsorption was proposed for the advanced treatment of biologically pretreated coking wastewater. Results of laboratory, pilot, and industrial-scale experiments indicated that this one-step novel process can remove biorefractory pollutants, achieving the maximum chemical oxygen demand (COD) and cyanide removals of around 85.3% and 99.4%, respectively. Its effluent could meet the corresponding discharge standards without any further treatment, i.e., COD <30mg/L, cyanide <0.1mg/L, and improved effluent safety (lower toxicity). The easy operation and high efficiency of this method reflect its engineering-application potential in the tertiary treatment of coking wastewater.

Selecting an appropriate method to remove cyanide from the wastewater of Moteh gold mine using a mathematical approach.

The presence of cyanide ions in wastewater is dangerous to the health and life of living creatures, especially humans. Cyanide concentration should not exceed the acceptable limit in wastewaters to avoid their adverse effects to the environment. In this paper, in order to select the most appropriate method to remove cyanide from the wastewater of the Moteh gold mine, based on the experts' opinions, the use of calcium hypochlorite, sodium hypochlorite, and hydrogen peroxide was chosen as forerunning alternative in the form of a multi-stage model. Then, seven criteria including the amount of material consumed, ease of implementation, safety, ability to remove cyanide, pH, time, and cost of the process to assess the considered methods were determined. Afterwards, seven experts conducted numerous experiments to examine the conditions of each of these criteria. Then, by employing a mathematical method called "numerical taxonomy," the use of sodium hypochlorite was suggested as the best method to remove cyanide from the wastewater of the Moteh gold mine. Finally, the TOPSIS model was used to validate the proposed model, which led to the same results of the suggested method. Also, the results of employing taxonomic analysis and TOPSIS method suggested the use of sodium hypochlorite as the best method for cyanide removal from wastewater. In addition, according to the analysis of various experiments, conditions for complete removal of cyanide using sodium hypochlorite included concentration (8.64 g/L), pH (12.3), and temperature (12 °C).

Quick and efficient co-treatment of Zn(2+)/Ni(2+) and CN(-) via the formation of Ni(CN)4(2-) intercalated larger ZnAl-LDH crystals.

The wide use of metal electroplating involving CN(-) necessitates the cost-effective treatment of both CN and metals (Zn, Cu, Ni etc.). In this research, we developed a novel strategy - Ni(2+)-assisted layered double hydroxide (LDH) precipitation - to simultaneously remove aqueous CN and Zn/Ni metals. The strategy is to convert CN(-)/Zn(CN)4(2-) to Ni(CN)4(2-) first, and then to quickly precipitate Ni(CN)4(2-)/CN(-) into LDH crystals. The conversion has been clearly evidenced by the change of CN characteristic FTIR bands of Zn-CN solution before and after adding Ni(NO3)2. The intercalation and efficient removal of CN have also been confirmed through the formation of LDH crystals XRD and SEM. In particular, a set of optimized experimental factors has been obtained by investigating their effects on CN removal efficiency in the simulated tests. Remarkably, over 95% CN were removed with high removal efficiencies of metals. Our results thus suggest that the current strategy is a quick, efficient and promising way to simultaneously treat both Ni and metals/CN rich electroplating wastewaters.