Removal of Uranium from Aqueous Solutions using Ammonium-modified Zeolite

Batch experiments were conducted to study the effects of contact time, pH (3 to 8), initial concentration, presence of carbonate, sulphate, and competing ions (Fe3+, Ca2+, Sr2+, Mg2+) on the adsorption of U(VI) on ammonium-modified zeolite (AMZ). The structural features of the modified zeolite were assessed by Fourier Transform Infra Red Spectroscopy (FTIR) while the metal content was determined by Inductively Coupled Plasma Optical Emission Specroscopy (ICP-OES). The removal of uranium was effective and maximal under acidic conditions (pH 3 to 5). The kinetics of adsorption of U-nitrate and U-sulphate on AMZ were described by the pseudo-second-order model (R2 ≥ 0.9820). In the presence of SO4 2- and CO3 2-, a significant reduction of 67.88 % and 71.63 %, respectively, in uranium uptake was observed. The distribution coefficient, KD (L g-1), was in the order of: U-nitrate (1.116) > U-sulphate (0.029) > U-carbonate (0.019), suggesting that AMZ had a high affinity for U-nitrate. The presence of Fe3+ enhanced the removal of U(VI) from U-nitrate, U-sulphate and U-carbonate by 20.18 %, 72.48%and 82.43 %, respectively, while the presence of Ca2+, Mg2+ and Sr2+ reduced the removal to 19.57 %, 31.60 % and 23.65 %, respectively. AMZ is an effective adsorbent for uranium removal from aqueous solutions dominated by nitrate, carbonate and sulphate.KEYWORDS Adsorption, zeolite-ammonium, uranyl, carbonate, sulphate, nitrate, aqueous solutions

Removal of uranium from aqueous solutions using ammonium-modified zeolite

Batch experiments were conducted to study the effects of contact time, pH (3 to 8), initial concentration, presence of carbonate, sulphate, and competing ions (Fe3+, Ca2+, Sr2+, Mg2+) on the adsorption of U(VI) on ammonium-modified zeolite (AMZ). The structural features of the modified zeolite were assessed by Fourier Transform Infra Red Spectroscopy (FTIR) while the metal content was determined by Inductively Coupled Plasma Optical Emission Specroscopy (ICP-OES). The removal of uranium was effective and maximal under acidic conditions (pH 3 to 5). The kinetics of adsorption of U-nitrate and U-sulphate on AMZ were described by the pseudo-second-order model (R2 ≥ 0.9820). In the presence of SO4 2- and CO3 2-, a significant reduction of 67.88 % and 71.63 %, respectively, in uranium uptake was observed. The distribution coefficient, KD (L g-1), was in the order of: U-nitrate (1.116) > U-sulphate (0.029) > U-carbonate (0.019), suggesting that AMZ had a high affinity for U-nitrate. The presence of Fe3+ enhanced the removal of U(VI) from U-nitrate, U-sulphate and U-carbonate by 20.18 %, 72.48 % and 82.43 %, respectively, while the presence of Ca2+, Mg2+ and Sr2+ reduced the removal to 19.57 %, 31.60 % and 23.65 %, respectively. AMZ is an effective adsorbent for uranium removal from aqueous solutions dominated by nitrate, carbonate and sulphate.SP201

Cyanide and cyanide complexes in the goldmine polluted land in the East and Central Rand Goldfields, South Africa

The use of cyanide in gold extraction is of concern when it is not properly managed from the extraction process to the management of wastes. The distribution and fate of cyanide in the environment upon release from the tailings dumps depends on its physical-chemical speciation. This study presents results of distribution, speciation and fate of cyanide in selected compartments, namely: tailings, sediments and water systems in gold mine polluted land. Sampling of tailings in a facility that is being rehabilitated was done in 2006 and 2007 to assess the impact of AMD on cyanide release over that period. Deposition of materials in the tailings dams stopped in 2004. The results revealed that the pH of the tailings decreased between 2006 and 2007. Elevated concentrations of CNfree, SCN- and CNO- were observed for 2007 compared to 2006. Most cyanide species had degraded as a result, primarily, of decrease in pH due to generation of AMD, also the oxidation of CNfree and the reaction with active sulphur species such as S2O3. The decrease of cyanide total (CNT) with time is a consequence of natural attenuation of cyanides in tailings which may be attributed to physicalchemical and microbiological mechanisms. Cyanide and its metal complexes were found to be unstable following generation of AMD in the dump over a period of one year. The dissociation of metal-cyanide complexes when the pH drops, releases CNfree which is either volatilised as HCN(g) or transported in solution with the contamination plume or converted to SCN- ,CNO- and NH4 +. However, in most of cases high concentrations of metal-cyanide complexes were found even at low pH values of the tailings suggesting that these complexes are very stable. This was substantiated by the geochemical modelling which predicted the predominance of iron-cyanide complexes in tailings at low pH. iii Cyanide released from cyanide complexes flows into the central pond of the tailings facility and partly leaches into the groundwater. Salt crusts were observed along the capillary fringe of the central pond as well as around other water bodies considered in the study. These crusts were found to contain elevated concentrations of heavy metals (e.g. 12940 mg kg-1 Fe and 186.1 mg kg-1 Co) and cyanide (e.g. 118.4 mg kg-1 CNT, 14.36 mg kg-1 CNWAD and 100.2 mg kg-1 CNSAD). This obviously has implications of secondary pollution as these crusts tend to be very soluble in water thus leading to the release of heavy metals and cyanide into water systems during rainfall. Characterization of cyanide was also done in drainage water from an active slimes dam where deposition from a reprocessing plant takes place. The slimes dam had drainage pipes and a solution trench around it that drained away excess water. Low concentration of CNT was obtained in pipe water from the pipe with low pH values (2 - 4) whilst this concentration was high in water from the trench with high pH values (5 -7). Copper and iron complexes were the most abundant. High concentrations of SCN- and CNO- were obtained as result of conversion of CNfree as explained previously. Salt crusts collected around the dam presented low pH (3) and high conductivity, the evidence of high metals content. High concentrations (198.4 mg kg-1) of CNT were obtained in the crusts with predominance of CNSAD (Fe and Co). The bluish-green colour of the crusts and the elevated concentrations of CNSAD as well as those for iron could suggest the presence of Prussian blue. Analysis of the wetland sediments showed the transport of cyanide from the tailings dumps to the wetland through the streams. An enrichment of cyanide was observed in the sediment with the enrichment factor of 3 for CNT with predominance of strong complexes (Fe and Co). The sediment is rich in organic matter and cyanide is known to bind strongly with organic matter. Although other possible sources (e.g. bacterial or microbial sources) could have contributed to the enrichment of cyanide in sediment, this was not investigated. Cyanide can be transported from the tailings dams to natural streams and other surface water bodies through groundwater. A natural stream within a reprocessing area was considered as a water system and cyanide in it was characterised. Three clusters were observed: water collected upstream with high pH, water from downstream with low pH (4) and the groundwater with low pH (3). Low concentrations of CNfree were obtained downstream. This could be due by the lost of CNfree by volatilization due acidic pH conditions. CNT was found to be lower downstream than upstream with the predominance of CNWAD. CNT concentrations were high at the seepage point, where the groundwater discharges to the surface. These concentrations were similar to those obtained in the groundwater. Copper and iron complexes were dominant in the surface and groundwater and this was substantiated by modelling results as well. SCN- was not detected in surface water as it is highly soluble in water and then leaches in the groundwater. The concentrations of CNO- were the same up and downstream. The results obtained from the study revealed that concentration of CNfree in most water bodies exceeded stipulated limits by bodies such as WHO, USEPA and UE. For instance, concentrations of up to 0.304 mg l-1 of CNfree were obtained in some instances to compare with limits of 0.07 mg l-1 by WHO, 0.02 mg l-1 by DWAF/South Africa. Additional studies should be done to find out the impact of organic matter (e.g. humic and fulvic acids) on the fate of cyanide. Various natural attenuation mechanisms of cyanide in tailings dams should be investigated. An assessment of the phytoremediation program vis-à-vis cyanide cyclisation is recommended and a monitoring of groundwater (borehole water) quality is required

Kinetic, equilibrium and thermodynamic modelling of the sorption of metals from aqueous solution by a silica polyamine composite

Batch sorption studies were conducted to assess the potential of a phosphonated silica polyamine composite (BPAP) to remove metals (Co, Cu, Fe, Mg, Mn, Ni, U and Zn) from mine waters. The metal adsorption showed a good Langmuir isotherm fit. Ni and Mn fitted both the Freundlich and Langmuir isotherms. The activation energies (Ea) of Co, Mg and Ni ranged between 5 and 40 kJ∙moℓ-1, signifying physisorption while U showed a chemisorption type of adsorption (with Ea > 50 kJ∙moℓ-1). Cu and Fe on the other hand gave negative Ea values, indicating their preference to bind to low-energy sites. The pseudo-second-order kinetic model provided the best correlation of the experimental data, except for Mg and Ni for which the pseudo-first-order model and the Elovich model gave a better fit, respectively. Adsorption was almost constant over a wide pH regime and increased with time. Adsorption increased with concentration of the metals with the exception of Co, Fe and Ni which displayed about a 40% drop at a concentration of 200 mg∙ℓ-1. Desorption experimental data gave poor results except for U which showed 99.9% desorption.Keywords: silica polyamine composite, sorption, kinetics, isotherms, desorptio

Formulation of zeolite supported nano-metallic catalyst and applications in textile effluent treatment

Textile industry is one of the major industries worldwide and produces a huge amount of coloured effluents. The presence of coloured compounds (dyes) in water change its aesthetic value and cause serious health and environmental consequences. However, the present investigation was carried out to minimize and reduce the colour compounds discharged by the textile industries through a nano-scaled catalyst. This study is mainly focused on the explanation of nanoparticles aggregation by deposition on natural zeolite, and utilization of this natural zeolite as supported material to nano zerovalent iron (NZ-nZVI) in the form of liquid slurry with sodium percarbonate acting as an oxidant in a Fenton like system for the removal of synthetic CI acid orange 52 (AO52) azo dye, in textile effluent. The nano-scaled zerovalent irons were synthesized by borohydride method in ethanolic medium. UV–vis spectrophotometry, FTIR, EDX, SEM, and XRD (powdered) analysis were used for the investigations of surface morphology, composition, and properties of natural zeolite supported nZVI and study the dye removal mechanism. The XRD spectrum revealed that clinoptilolite is the major component of natural zeolite used, while EDX found that the iron content of NZ-nZVI was about 9.5 %. The introduction of natural zeolite as supporting material in the formation of iron nanoparticle resulted in the partial reduction of aggregation of zerovalent iron nanoparticles. The findings revealed that the 94.86 % removal of CI acid orange 52 dye was obtained after 180 min treatment at 15 mg/L initial dye concentration. The highest rapid dye removal of about 60 % was achieved within the first 10 min of treatment at the same dye concentration. Furthermore, the actual dyeing effluent including green, magenta, and the blended colour was successfully decolourized by natural zeolite-supported nZVI/SPC Fenton process. It is concluded that the acceleration of corrosion of NZ-nZVI, breaking of azo bond, and consumption of Fe2+ were the possible mechanisms behind the removal of AO52 dye. It is also recommended that NZ-nZVI/SPC Fenton process could be a viable option for effluent and groundwater remediation

Effect of biochar modified with magnetite nanoparticles and HNO\u3csub\u3e3\u3c/sub\u3e for efficient removal of Cr(VI) from contaminated water: A batch and column scale study

© 2020 Elsevier Ltd Chromium (Cr) poses serious consequences on human and animal health due to its potential carcinogenicity. The present study aims at preparing a novel biochar derived from Chenopodium quinoa crop residues (QBC), its activation with magnetite nanoparticles (QBC/MNPs) and strong acid HNO3 (QBC/Acid) to evaluate their batch and column scale potential to remove Cr (VI) from polluted water. The QBC, QBC/MNPs and QBC/Acid were characterized with SEM, FTIR, EDX, XRD as well as point of zero charge (PZC) to get an insight into their adsorption mechanism. The impact of different process parameters including dose of the adsorbent (1–4 g/L), contact time (0–180 min), initial concentration of Cr (25–200 mg/L) as well as solution pH (2–8) was evaluated on the Cr (VI) removal from contaminated water. The results revealed that QBC/MNPs proved more effective (73.35–93.62-%) for the Cr (VI) removal with 77.35 mg/g adsorption capacity as compared with QBC/Acid (55.85–79.8%) and QBC (48.85–75.28-%) when Cr concentration was changed from 200 to 25 mg/L. The isothermal experimental results follow the Freundlich adsorption model rather than Langmuir, Temkin and Dubinin-Radushkevich adsorption isotherm models. While kinetic adsorption results were well demonstrated by pseudo second order kinetic model. Column scale experiments conducted at steady state exhibited excellent retention of Cr (VI) by QBC, QBC/MNPs and QBC/Acid at 50 and 100 mg Cr/L. The results showed that this novel biochar (QBC) and its modified forms (QBC/Acid and QBC/MNPs) are applicable with excellent reusability and stability under acidic conditions for the practical treatment of Cr (VI) contaminated water