Initial Cyanide Concentration Research Articles

Adsorption of cyanide from Cassava wastewater using activated carbons derived from Raphia hookeri kernels: a comparison of in-situ and ex-situ activation

The rise in cyanide concentration in groundwater in many developing countries is linked to the indiscriminate discharge of cyanide-bearing wastewater from cassava processing industries. This research synthesized a super-active activated carbon (AC) from a novel biomass precursor, Raphia hookeri kernel, functionalized with phosphoric acid via in-situ and ex-situ methods. Morphological and functional characterizations were performed, and the influence of some key process variables on cyanide adsorption was also investigated for the two derived ACs to study the impact of the activation method used. The optimal conditions for cyanide adsorption for the in-situ and ex-situ–derived ACs were identified as pH 8, AC dose of 0.15 g, temperature of 40 °C, and initial cyanide concentration of 100 mgL−1 at different equilibrium times of 100 min and 120 min, respectively. The kinetic studies revealed that the pseudo-second-order kinetic model fitted the adsorption data better for the two ACs based on the high correlation coefficients (r2), suggesting that the adsorption process is chemisorption. The equilibrium studies showed that the in-situ-derived AC followed the Langmuir isotherm with a maximum adsorption capacity (qm) of 93.821 mgg−1 indicating monolayer adsorption for the in-situ-derived AC. The ex-situ-derived AC, however, followed the Sips isotherm with a maximum adsorption capacity (qm) of 79.381 mgg−1 indicating a heterogeneous surface for the ex-situ-derived AC. The ACs showed decreasing cyanide adsorption after five cycles but maintained significant adsorption capacity after desorption-adsorption cycles.

Synthesis and characterization of hydroxyapatite derived from waste chicken eggshells for cyanide removal application

In the present study, hydroxyapatite (HAp) was synthesized from waste chicken eggshells using wet chemical precipitation method. The entire process involved the conversion of raw chicken eggshells to calcined form to finally HAp via precipitation. The functional groups in the synthesized sample were determined by Fourier Transform Infrared Spectroscopy (FTIR) analysis. HAp was also characterized using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) to describe its morphology and elemental composition, respectively. The potential of HAp for cyanide removal in aqueous solution was further investigated via batch sorption with 3 × 2 factorial experimental design to determine the effects of initial cyanide concentration and HAp dosage. The highest percent removal was 50.31% attained at 64 mg L−1 cyanide concentration and 0.3 g HAp dosage after a 30-min contact time with solution pH maintained within the range 8.5–9.5. Two-way ANOVA results show significant main and interaction effects of the varied factors to the cyanide removal efficiency at 95% confidence level.

Optimization and Modeling of Cyanide Removal from Cassava Waste Water Using Calcined and Activated Adsorbent Mixtures of Oyster Shell and Periwinkle Shell Ash

Cyanide, a toxic compound found in cassava wastewater which on frequent basis is discharged to the environment poses danger to the ecosystem; this research work aims to curb this menace. Temperature, pH, dosage, contact time, adsorbent mixture ratio and initial concentration were optimized using CCD on periwinkle-oyster shells composite mixtures for activated and also, calcined adsorbents on the cyanide adsorption from cassava wastewater. Three RSM models (linear, 2FI and quadratic) were applied to study, optimize and predict this adsorption process. ANOVA showed that quadratic model best predicted the processes for both the activated and calcined adsorbents having R2 values of 0.9678, CV% of 15.51% for the activated and R2 values of 0.9550, CV% of 18.54% for the calcined composite adsorbent. Surface and contour plots were generated to study the interaction between the adsorption parameters and cyanide adsorption. Results from this study also show that pH and initial cyanide concentration were the most determining factors of the adsorption process for both adsorbent samples with the highest adsorption capacity of 96.648% and 96.112% obtained for the activated and calcined composite adsorbent respectively. Numerical optimization was carried out and the confirmation test on the analyzed best-fit quadratic models yielded actual adsorption efficiency of 90.174% as against the predicted adsorption efficiency of 89.83% for the activated and actual adsorption efficiency of 82.274% as against the predicted adsorption efficiency of 83.475% for the calcined composite adsorbent hence, confirms that both activated and calcined adsorbents of oyster-periwinkle shells composite mixture is effective for cyanide adsorption from cassava wastewater and the RSM models were effective to optimize and predict the process.

Behavior and mechanism of cyanide loss in ultrasound-assisted gold leaching process

The potential effect of ultrasound was investigated, which could lead to cyanide loss or decomposition during gold leaching. The variations of cyanide concentration during gold leaching with and without ultrasound were compared. The influence of initial cyanide concentration, pH, temperature, atmosphere, natural loss, hydrolysis, and cavitation effect on the loss of cyanide was examined. The results showed that the loss of cyanide was mainly caused by hydrolysis, oxidation, and reaction with CO2 in the traditional gold leaching process. With the introduction of ultrasound, the oxidative •OH slightly increased the loss of cyanide. Comparing the concentration variations of total cyanide and free cyanide proved that ultrasound (120 W) exhibited a non-detrimental effect on the loss of cyanide in gold leaching process.

Prebiotic synthesis of noncanonical nucleobases under plausible alkaline hydrothermal conditions

Herein, the potential of alkaline hydrothermal environments for the synthesis of possible ancestral pre-RNA nucleobases using cyanide as a primary source of carbon and nitrogen is described. Water cyanide polymerizations were assisted by microwave radiation to obtain high temperature and a relatively high pressure (MWR, 180 °C, 15 bar) and were also carried out using a conventional thermal system (CTS, 80 °C, 1 bar) to simulate subaerial and aerial hydrothermal conditions, respectively, on the early Earth. For these syntheses, the initial concentration of cyanide and the diffusion effects were studied. In addition, it is well known that hydrolysis conditions are directly related to the amount and diversity of organic molecules released from cyanide polymers. Thus, as a first step, we studied the effect of several hydrolysis procedures, generally used in prebiotic chemistry, on some of the potential pre-RNA nucleobases of interest, together with some of their isomers and/or deamination products, also presumably formed in these complex reactions. The results show that the alkaline hydrothermal scenarios with a relatively constant pH are good geological scenarios for the generation of noncanonical nucleobases using cyanide as a prebiotic precursor.

Purifying cyanide-bearing wastewaters by electrochemical precipitate process using sacrificial Zn anode

With the rapid development of society, wastewaters, such as cyanide-containing wastewaters (CBWs) have caused environmental problems. In the present work, an electrochemical approach using sacrificial Zn anode was investigated for the removal of cyanides from CBWs. The effects of operational parameters, such as current density, pH, initial cyanide concentration, and ionic strength, on the cyanides removal from synthetic solution were discussed in turn. Under the optimal conditions obtained, the treatment of industrial CBWs was considered. Subsequently, more attentions were paid to elucidate the removal mechanisms of cyanide ions and the corresponding metal-cyanide (copper and iron) complexes by a combination of cyclic voltammetry (CV), pHPZC, X-Ray diffractometer (XRD), scanning electron microscope with energy disperse spectroscopy (SEM/EDS) and X-ray photoelectron spectrometer (XPS) characterizations. Experimental results demonstrated that the removal efficiency of total cyanide (CNT), Cu, and Fe from industrial CBWs are 98%, 91%, and 96%, respectively, with an anode consumption of 1.78 kg/m3 and energy consumption of 2.50 kW·h/m3, of which 72% of Cu was collected on the cathode and almost all of Fe was in the precipitate. Removal mechanisms suggested that free cyanide (CN–) mainly presented as Zn(CN)2 into the electrolytic precipitate. The replacement of Zn2+ and electroreduction promoted 72% of Cu(I) to be reduced, while 57% of the remaining portion of Cu(I) was oxidized to Cu(II) and 43% of Cu(I) could form CuSCN into the precipitate by XPS analysis. With respect to Fe, it was mainly ascribed to the formation of Zn2Fe(CN)6 precipitate to be removed. From above, this work provided a method for enriching cyanides from wastewaters into the precipitate, while valuable metal Cu was deposited on the cathode, facilitating the separation and recovery of valuable resources.

Evaluation of N doped rGO-ZnO-CoPc(COOH)8 nanocomposite in cyanide degradation and its bactericidal activities

In the present study, an attempt has been made to design a solar light driven N-rGO-ZnO- CoPc(COOH)8 nanocomposite for the degradation of cyanide. The morphological and structural characterization of the synthesized nanocomposite was performed by XRD, FT-IR, XPS, UV–vis DRS, FESEM, TEM, EDS, PL spectra and BET surface area. The results revealed that almost 91% degradation and 86% toxicity removal occurred at 25 mgL−1 of initial cyanide concentration by the N-rGO-ZnO-CoPc(COOH)8 nanocomposite under illumination of solar light within 120 min. Analysis of free radicals reveals that the generation of OH. radicals was the predominant species in the photocatalytic degradation process. The cyanide degradation follows pseudo-first order kinetics. The estimated apparent rate constant (Kapp) of the above nanocomposite was 3 times higher than that of the ZnO photocatalyst alone together with a very good recycle activities. This might be due to the application of metallpthalocyanine photosensitizer CoPc(COOH)8 which enhances the rate of visible light absorption efficiency and activates the higher band gap ZnO photocatalyst under visible light. In addition, the presence of residual oxygen in N-rGO also promotes nucleation and anchor sites for interfacial contact between ZnO and N-rGO for effective charge transfer. Further, the N-rGO-ZnO-CoPc(COOH)8 photocatalytic system showed significant antibacterial activities against mixed culture systems. Therefore, the N-rGO-ZnO-CoPc(COOH)8 nanocomposite may be an alternative solar light driven photocatalyst system for the removal of cyanide from the wastewater along with its strong disinfectant activities.

Combined treatment based on synergism between hydrodynamic cavitation and H2O2 for degradation of cyanide in effluents

The main purpose of this research has been to evaluate and optimize the application of hydrodynamic cavitation (HC), combined with hydrogen peroxide, as a promising process for the effective degradation of cyanide in aqueous effluents. The experimental work was carried out using cavitation equipment with a venturi device connected to a tubular circuit which allowed a closed-cycle flow to run for 120 min, in which the effect of control parameters as inlet pressure, H2O2:CN─ ratio, pH, and temperature have been evaluated for the treatment of solutions with initial cyanide concentration in range 100 to 550 mg L─1.The results showed that in optimal conditions cyanide degradation using only HC reached 70% and, using solely H2O2 as oxidizing agent it reached 63%. Efficiency of the combined treatment process was evaluated on the basis of their synergetic effect as it turned out to be more effective showing a 99.9 % cyanide degradation in less than 120 min. The optimum set of conditions that produced the highest degradation rate and efficiency was: inlet pressure 4 bar; pH 9.5; and H2O2:CN─ ratio = 1.5:1. The process was also evaluated on the basis of cavitational yield and in terms of energy and chemical treatment costs. The results have demonstrated that the combined treatment technology of HC + H2O2 can be effectively used as a fast and highly efficient treatment of wastewater containing cyanide.

Phytoremediation potential of water hyacinth (Eichhornia crassipes) for phenol and cyanide elimination from synthetic/simulated wastewater

Water pollution is increasing due to urbanization and industrialization. Waste water pollution raised concern because of its influence on plants and humans. Water hyacinth (Eichhornia crassipes) is used for the removal of pollutants because of its phytoremediation efficiency. In this study, water hyacinth (Eichhornia crassipes) has been tested for simultaneous elimination of phenol and cyanide from mono and binary component aqueous solution in batch systems. The plant was grown at six concentrations of phenol and cyanide in the ratio of (10:1), i.e. 100:10, 200:20, 300:30, 500:50, 700:70 and 1000:100 mg/L in aqueous solution. The effect of process parameters such as initial concentration of phenol and cyanide and pH was evaluated. The plant was found capable of eliminating up to 96.42% of phenol (300 mg/L) and 92.66% of cyanide (30 mg/L) during the 13 days cultivation time at pH 8. The calculated Km of the root length elongation for phenol was 5.20 mm and the Vmax was 12.52 μg phenol/g root/h. However, the calculated Km of the root length elongation for cyanide was 0.39 mm and the Vmax was 14.99 μg cyanide/ g root/h. In the Eichhornia crassipes plant, the biochemical parameters such as chlorophyll, protein and sugar content have been indicated a decreasing trend due to uptake of phenol and cyanide throughout cultivation. Toxicity to 100–1000 mg/L of phenol and 10–100 mg/L of cyanide was measured by measuring the relative transpiration over 13 days. At 100 mg/L of phenol and 10 mg/L of cyanide, only a small reduction in transpiration but no morphological changes were noticed. Both pollutants are absorbed through the root of the Eichhornia crassipes plant by plasmalemma and become accumulated into the root cells and stem of a plant. Thus, this study will be beneficial for the decontamination of highly polluted waste water.

Predicting the capability of diatomite magnano composite boosted with polymer extracted from brown seaweeds for the adsorption of cyanide from water solutions using the response surface methodology: modelling and optimisation

ABSTRACT The rate of cyanide reduction in the aqueous solutions by adsorption onto the diatomite magnano composite boosted with alginate polymer beads (DMBA) was evaluated. The R software using RSM was used as an experimental technique to design a statistical equation. Based on statistical results obtained, second order model due to insignificant lack of fit (0.12) and the higher value of correlation coefficient (0.92) was selected as a suitable model to design of the adsorption process. Based on the stationary points, the maximum adsorption of cyanide (98.11%) was achieved under selected conditions (initial cyanide concentration, 4.88 mg L−1; contact time, 91.06 min and DMBA dosage, 2.05 g L−1). The Sips nonlinear model indicated the best compatibility with the experimental data. It was found to be a successful model for predicting the heterogeneity of surfaces. The maximum adsorption capacity of cyanide onto DMBA was determined 208.55 mg g−1. The pseudo-first-order model was found to agree well with the adsorption experimental data obtained for cyanide. The thermodynamic data revealed the spontaneous sorption and endothermic for the adsorption of cyanide onto DMBA.

Effects of physicochemical properties of Au cyanidation tailings on cyanide microbial degradation

The initial cyanide (CN−) concentration and amount of co-contaminants in GCTs can inhibit bacterial growth and reduce the CN−-degrading ability of bacteria. Several microorganisms can biotransform a wide range of organic and inorganic industrial contaminants into nontoxic compounds. However, active enzymatic CN− metabolism processes are mostly constrained by the physical and chemical characteristics of GCTs. High concentrations of toxic metal co-contaminants, such as, Pb, and Cr, and factors, such as pH, temperature, and oxygen concentration create oxidative stress and limit the CN−-degrading potential of cyanotrophic strains. The effects of such external and internal factors on the CN−-degrading ability of bacteria hinder the selection of suitable microorganisms for CN− biodegradation. Therefore, understanding the effects of the physicochemical properties of GCTs on cyanobacteria strains can help identify suitable microbes and favorable environmental conditions to promote microbial growth and can also help design efficient CN− biodegradation processes. In this review, we present a detailed analysis of the physicochemical properties of GCTs and their effects on microbial CN− degradation.

Biodegradation efficacy of coke oven wastewater inherent co-cultured novel sp. Alcaligenes faecalis JF339228 and Klebsiella oxytoca KF303807 on phenol and cyanide—kinetic and toxicity analysis

Coke oven sector emanates phenol and cyanide as the eminent virulent compounds due to abrupt industrialization which is detrimental in aqueous state, and its severity is increased on simultaneous coexistence even at low concentrations that eventually causes extensive damage to the peripheral ecosystem. The efficacy of isolated mixed bacterial culture comprising of Alcaligenes faecalis JF339228 and Klebsiella oxytoca KF303807 in wastewater treatment was investigated following a batch study. The impact of initial concentration of phenol (100–1500 mg L−1) and cyanide (10–150 mg L−1) on the growth and treatment by the mixed microbial cultures were evaluated over a time period of 72 h. The biodegradation mechanism was explained by Monod, Haldane, Aiba and Edward kinetic models. The maximum specific growth rate was reported to be 0.096 h−1 and 0.126 h−1 for phenol and cyanide respectively. The substrate inhibitory effect became eminent after a concentration of 450 mg L−1 for phenol and 45 mg L−1 for cyanide. Based on the lower sum of squared error (SSE) values, Haldane model for phenol and Edward model for cyanide was found to be favourable for substrate inhibition kinetics. The fate of the secondary intermediates produced after microbial degradation was assessed by phytotoxicity studies using Vigna radiata. The interactive binding of the pernicious pollutants and resultant biodegraded compounds with the DNA (herring sperm DNA) was examined following spectrofluorometric and spectrophotometric anatomization. Toxicity studies revealed that biological treatment was viable for eco benign disposal and results also depicted that both the strains have potential in remediation of phenol and cyanide from coke oven wastewater.

Experimental study on cyanide-contaminated soil (China) treatment by leaching and decomposition.

The removal of cyanide compounds in soil by leaching was investigated in flask and column tests. All the experiments were conducted under alkaline conditions to prevent loss of hydrogen cyanide. Results showed that leaching progressed rapidly when the leaching temperature or the initial cyanide concentration was high. The obtained cyanide data in the flask test fitted an inner diffusion process, as described by a shrinking core model. In the batch column test, the cyanide concentration decreased from 44.06 to 9.86mg/kg when the leaching intensity was 79L/(m2h) after 23.8h leaching. The leaching process for the cyanide compounds was divided into two stages according to the batch column test despite the decrease in the leaching velocity as the cyanide concentration in soil declined. Cyanide removal in the batch column test was better than that in the flask test due to the higher gradient of cyanide concentration. The aqueous solution containing cyanide compounds was decomposed effectively by the hybrid process of ozone and UV rays. Furthermore, the leaching and decomposition of the soil and leaching wastewater were performed with a continuous column test with circulating leaching liquid. The cyanide compounds in the soil and wastewater were removed effectively.

Mineralization of cyanide originating from gold leaching effluent using electro-oxidation: multi-objective optimization and kinetic study

This study examines the electro-oxidation (EO) of cyanide originating from an industrial plant´s gold leaching effluent. Experiments were carried out in a laboratory-scale batch cell reactor. Monopolar configuration of electrodes consisting of graphite (anode) and aluminum (cathode) was employed, operating in galvanostatic mode. Response Surface Methodology (RSM), based on a Box–Behnken experimental Design (BBD), was used to optimize the EO operational conditions. Three independent process variables were considered: initial cyanide concentration ([CN−]0 = 1000–2000 mg L−1), current density (J =7–107 mA cm−2), and stirring velocity (η = 250–750 rpm). The cyanide conversion $$\left( {X_{{{\text{CN}}^{ - } }} } \right)$$, Chemical Oxygen Demand (COD) removal percentage (%RCOD), and specific Energy Consumption per unit mass of removed cyanide (EC) were analyzed as response variables. Multi-objective optimization let to establish the most effective EO conditions ([CN−]0 = 1000 mg L−1, J = 100 mA cm−2 and η = 750 rpm). The experimental data ($$X_{{{\text{CN}}^{ - } }}$$, %RCOD, and EC) were fitted to second-order polynomial models with adjusted correlation coefficients ($$R_{\text{adj}}^{2}$$) of ca. 98, 99 and 87%, respectively. The kinetic analysis, performed at optimal EO operational conditions, allowed determination of time required to meet Colombian permissible discharge limits. The predictive capacity of kinetic expressions was verified against experimental data obtained for gold leaching effluent. Total cyanide removal and 96% of COD reduction were obtained, requiring EC of 71.33 kWh kg−1 and 180 min. The BOD5 (biological oxygen demand)/COD ratio increased from 4.52 × 10−4 to 0.5573, confirming effluent biodegradability after EO treatment. The variation of cyanide (CN−), cyanate (CNO−) and ammonium (NH4+) ions concentrations vs. time at alkaline conditions. EO operational conditions: [CN−]0 = 1000 mg/L, J = 100 mA/cm2 , η = 750 rpm, [NaCl] = 0.15 M and pH 11.1.

Treatment of tapioca starch wastewater with ozonation and adsorption

In this research, removal of cyanide and COD in tapioca starch wastewater by ozonation and adsorption using GAC examined. The method effectiveness evaluated from percentage of cyanide and COD degradation and ozone mass balance. Effect of degradation method, pH and ozone dose was determined using synthetic wastewater with initial cyanide concentration of 30 ppm and COD concentration of 1000 ppm. Using ozonation adsorption with pH 10 and ozone generation rate of 303 mg O3/h, 91.75% cyanide and 68.94% COD from synthetic wastewater was removed in 1 hour. Tapioca starch wastewater with cyanide concentration of 8.5 ppm and COD concentration of 4625 ppm treated using the same operating condition. Using this method, 87.06% cyanide and 43.23% COD was removed.

Cyanide adsorption from cassava wastewater onto calcined periwinkle shell

Local cassava processing industries produce large quantities of wastewater containing cyanide which is toxic in nature with negative impacts on the environment when disposed without treatment. In this study calcined periwinkle shell (CPS) was prepared, characterized and used to adsorb cyanide present in cassava wastewater. Equilibrium studies were conducted in batch set ups to investigate the influence of process variables such as adsorbent dosage, pH, temperature, contact time and initial cyanide concentration on the adsorption process. The highest removal rate of cyanide from cassava wastewater was found to be 78.34% with equilibrium reached at fixed adsorbent dosage of 3.0 g at contact time of 80 minutes. Cyanide adsorption was also observed to be dependent on pH with the maximum adsorption of cyanide occurring at a pH 10. The percentage of cyanide removed decreased with increase in cyanide concentration. Results from the study confirm calcined periwinkle shell as low cost and effective adsorbent which can be used for the removal of cyanide from cassava wastewater

The effect of thermal and acid treatment of kaolin on its ability for cyanide removal from aqueous solutions

The removal of free cyanide from aqueous solutions was investigated by kaolin, calcined kaolin (metakaolin), and acid-treated metakaolin. The kaolin in raw form had no ability for cyanide adsorption, but calcination and acid treatment significantly improve its adsorptive properties. The best calcination conditions were determined to be at temperature of 600 °C and calcination time of 1 h. The scanning electron microscope (SEM), wavelength-dispersive X-ray (WDX), X-ray fluorescence (XRF), and X-ray diffraction (XRD) analysis methods were used to explain the adsorptive properties of the adsorbents. The loading capacity of metakaolin increased from 0.66 to 5.32 mg/g, and the loading capacity of acid-treated metakaolin increased from 1.33 to 10.67 mg/g by increasing the initial cyanide concentration from 25 to 531 mg/L. The kinetics of cyanide adsorption onto both adsorbents increases by increasing the initial cyanide concentration (25–531 mg/L) and solution temperature (30–50 °C). The equilibrium and kinetic data on both adsorbents are best fitted by the Freundlich isotherm and pseudo-second-order kinetic models, respectively. The thermodynamic study showed that the cyanide adsorption onto both adsorbents is endothermic and spontaneous in nature. The activation energy for the cyanide adsorption onto metakaolin and acid-treated metakaolin was determined to be 16.68 and 5.79 kJ/mol which indicates that the adsorption of cyanide ions onto metakaolin is chemisorption and onto the acid-treated metakaolin is a physicochemical process.

Adsorption of Cyanide from Cassava Wastewater Using Calcined and Activated Oyster Shell Ash

Calcined ash and activated ash adsorbents were prepared from oyster shell. The physico-chemical properties of the prepared calcined oyster shell ash (COSA) and activated oyster shell ash (AOSA) were obtained using ASTM standards and Sears method. The results show that AOSA is a better adsorbent for removal of cyanide from cassava wastewater than COSA. The adsorption of cyanide from cassava wastewater onto adsorbents (COSA and AOSA) was investigated as a function of pH, adsorbent dosage, contact time, temperature and initial cyanide concentration. The batch study reveals that the adsorption process is strongly pH dependent and maximum cyanide removal is found to occur at pH of 10. The highest percent removal of cyanide from cassava wastewater was found at contact time of 80 minutes and 30oC. The effect of temperature on the adsorption process shows a small increase in the percent cyanide removal followed by a large decrease which suggests physical adsorption as the adsorption mechanism. The percent cyanide removal efficiency decreases with increase in initial cyanide concentration and increases with increase in adsorbent dosage.

A cost-effective approach for abatement of cyanide using iron-impregnated activated carbon: kinetic and equilibrium study

The present study is devoted for eliminating cyanide from wastewater through adsorption onto a surface impregnated with iron. It is seen that the impregnation of iron improves the removal efficacy of cyanide. Ferric nitrate nonahydrate has been used as impregnating agent, and Corncob, a waste material, has been used as a progenitor for the preparation of adsorbent. For determining the optimum conditions for impregnation of iron, response surface methodology has been employed. Combined effect of weight ratio, time, and temperature has been tested, and optimum condition has been obtained with weight ratio (1.0), time (1.50 h), and temperature (400 °C), and the sample made at this condition is named as iron-impregnated activated carbon (IIAC). While studying the adsorptive behavior of IIAC in contrast to activated Corncob without impregnation (ACWI), it has been found that for a cyanide solution of 50 mg L−1, ACWI can remove only 61% of cyanide and IIAC is able to remove around 91% at a constant adsorbent dosage of 10 g L−1. The minimum (− 1) and maximum (+ 1) level of particle sizes (45–150 µm), adsorbent dosage (5–20 g L−1), and initial concentration (IC) of cyanide (5–50 mg L−1) on cyanide removal have been examined using ANOVA, at room temperature (25 °C) for knowing the dependence on the same. Maximum cyanide removal (99.58%) has been achieved at an optimum particle size of 100 µm, adsorbent dosage of 3.95 g L−1, IC of 27.5 mg L−1 at pH 7.5 with IIAC. Langmuir and Freundlich isotherm models have been used for analyzing equilibrium data where Freundlich isotherm has been suitable. Different kinetic models have been employed to fit the data. Pseudo-second-order kinetic model has been found to be most applicable.

Enhanced photocatalytic degradation of cyanide employing Fe-porphyrin sensitizer with hydroxyapatite palladium doped TiO2nano-composite system

The current research paper deals with the study of palladium doped TiO2 based photocatalytic system to remove cyanide from coke oven wastewater. The photocatalytic activity was improved by employing hydroxyapatite nanoparticles, which serves to enhance the concentration of cyanide near the photoactive sites of TiO2 and also prevents its agglomeration. Further, to enhance the rate of photocatalytic degradation of cyanide under visible light irradiation an iron tetracarboxy phenyl porphyrin sensitizer (Fe-TCPP) was employed. The structural and morphological characterization of the synthesized catalysts were carried out by Fourier transformation infrared spectroscopy (FTIR), X-ray diffraction (XRD), photoluminescence (PL) emission spectra, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and ultraviolet diffuse reflectance spectroscopy (UV- DRS). The photocatalytic activity of the TiO2-Pd-HAP-Fe-TCPP- nanocomposite has been evaluated on degradation of cyanide under visible light irradiation using a photocatalytic reactor system. The results demonstrate the existence of synergistic effect between TiO2-Pd-HAP and Fe-TCPP sensitizer on removal of cyanide. Almost 90% of cyanide degradation was achieved at pH 11 within a short time span of 90 min, using the TiO2-Pd-HAP -Fe-TCPP nanocomposite. The photocatalytic degradation of cyanide by the nanocomposite follows pseudo-first order kinetics. The apparent rate constant (kapp) value of the TiO2-Pd-HAP-Fe-TCPP nanocomposite is estimated to be 11.6 and 4.3 time higher than that of bare TiO2 and TiO2-Pd-HAP respectively. Further, at this condition, >90% toxicity removal was achieved in the photocatalytic system even at a very high initial concentration of cyanide. Therefore, the Fe-TCPP-TiO2-Pd-HAP nanocomposite system can be considered as an alternative technique for removal of cyanide from coke oven wastewater.