The effect of zinc ion concentration and pH on the leaching kinetics of calcined zinc oxide ore

Previous studies on the dissolution of zinc oxide have concentrated on the effects of temperature, reagent concentration, particle size and agitation rate, among other factors. However, there is dearth data on the effect of a combination of product concentration and pH on leaching rates. This work examines the effects of the concentration of pH and zinc ions on the dissolution kinetics of zinc oxide. The results showed that the rate of zinc dissolution was greatest at lower pHs. This is because at lower pH, the concentration of acid (H+ ions) is also expected to be high (pH = log10[H+]), thus increasing the reaction kinetics in accordance with the kinetic molecular theory. The rate of reaction was found to increase with an increase in the concentration of zinc ions (Zn2+), which is in contrast to established theories. This observation can be explained by the fact that since heat energy produced (via an exothermic reaction) was continuously being dissipated through a constant temperature water bath it favoured zinc oxide dissolution. Zinc oxide ore at 62.5% purity also comprised of other metal oxides (e.g., iron, copper, manganese, etc) which were simultaneously leached. Since the solution was recycled, the concentration of iron, for example, could have also increased. Since zinc is more reactive than iron, two reaction mechanisms could have possibly been occurring at the same time, i.e., the dissolution of zinc oxide ore by sulfuric acid and the displacement of iron in solution by zinc in zinc oxide forming iron hydroxide

Engineered nanoparticle bio-conjugates toxicity screening: The xCELLigence cells viability impact

Introduction: The vast diverse products and applications of engineered nanoparticle bio-conjugates (ENPBCs) are increasing, and thus flooding the-markets. However, the data to support risk estimates of ENPBC are limited. While it is important to assess the potential benefits, acceptability and uptake, it is equally important to understand where ENPBCs safety is and how to expand and affirm consumer security concerns. Methods: Online articles were extracted from 2013 to 2016 that pragmatically used xCELLigence real-time cell analysis (RTCA) technology to describe the in-vitro toxicity of ENPBCs. The xCELLigence is a +noninvasive in vitro toxicity monitoring process that mimics exact continuous cellular bio-responses in real-time settings. On the other hand, articles were also extracted from 2008 to 2016 describing the in vivo animal models toxicity of ENPBCs with regards to safety outcomes. Results: Out of 32 of the 121 (26.4%) articles identified from the literature, 23 (71.9%) met the in-vitro xCELLigence and 9(28.1%) complied with the in vivo animal model toxicity inclusion criteria. Of the 23 articles, 4 of them (17.4%) had no size estimation of ENPBCs. The xCELLigence technology provided information on cell interactions, viability, and proliferation process. Eighty-three (19/23) of the in vitro xCELLigence technology studies described ENPBCs as nontoxic or partially nontoxic materials. The in vivo animal model provided further toxicity information where 1(1/9) of the in vivo animal model studies indicated potential animal toxicity while the remaining results recommended ENPPCs as potential candidates for drug therapy though with limited information on toxicity. Conclusion: The results showed that the bioimpacts of ENPBCs either at the in vitro or at in vivo animal model levels are still limited due to insufficient information and data. To keep pace with ENPBCs biomedical products and applications, in vitro, in vivo assays, clinical trials and long-term impacts are needed to validate their usability and uptake. Besides, more real-time ENPBCs-cell impact analyses using xCELLigence are needed to provide significant data and information for further in vivo testing

Phase equilibrium of volatile organic compounds in silicon oil using the UNIFAC procedure : an estimation

This paper focuses on the phase equilibrium of volatile organic compounds in silicon oil chemically known as PDMS (polydimethylsiloxane) at infinite dilution. Measurements can be expensive and time consuming, hence the need for thermodynamic models which allow the calculation of the phase equilibrium behavior using a limited number of experimental data. The objective of this study was to predict infinite dilution activity coefficients of selected VOCs (volatile organic compounds) in PDMS using the Original UNIFAC model. The predicted results show that PDMS can be used to abate volatile organic compounds from contaminated air streams. The results obtained in this work are comparable to those obtained by the same authors through measurements such as the static headspace and the dynamic gas liquid chromatographic techniques as well as other literature. Although the UNIFAC group contribution method over estimate the infinite dilution activity coefficients, the results of this work may be applied in preliminary phases of process design, simulation and feasibility studies

Adsorptive removal of BTEX compounds from wastewater using activated carbon derived from macadamia nut shells

In this study, adsorptive removal of benzene, toluene, ethylbenzene and xylenes (BTEX) from synthetic water using activated carbon adsorbent derived from macadamia nut shells was investigated. The surface  functional groups of the synthesized adsorbents were assessed by Fourier transform infrared spectra. The specific surface area, pore size and pore volume at 77 K nitrogen adsorption, surface morphology, and the crystalline structure of the adsorbents were determined using Brunauer-Emmett-Teller, scanning electron microscopy and x-ray diffraction, respectively. Batch adsorption mode was used to evaluate the performance of the activated carbon. The stock solutions of synthetic wastewater were prepared by dissolving 100 mg/L of each of the BTEX compound into distilled water in a 250 mL volumetric flask. Effect of initial concentration of BTEX compounds, contact time, and mass of adsorbent on the removal of BTEX compounds from the synthetic wastewater was investigated. The macadamia nut shell–derived activated carbon (MAC) proved to be an effective adsorbent for BTEX compounds, with a large surface area of 405.56 m2/g. The exposure time to reach equilibrium for maximum removal of BTEX was observed to be 20 min. The adsorption capacity of the BTEX compounds by MAC followed the following adsorption order: benzene > toluene > ethylbenzene > xylene.&nbsp

The heterogeneous coagulation and flocculation of brewery wastewater using carbon nanotubes

Coagulation and flocculation treatment processes play a central role in the way wastewater effluents are managed. Their primary function is particle removal that can impart colour to a water source, create turbidity, and/or retain bacterial and viral organisms. This study was carried out to investigate whether carbon nanotubes (CNTs) can be used as heterogeneous coagulants and/or flocculants in the pretreatment of brewery wastewater. A series of experiments were conducted in which the efficiencies of pristine and functionalised CNTs were compared with the efficiency of traditional ferric chloride in a coagulation/flocculation process. Turbidity and chemical oxygen demand (COD), including the zeta potential were used to monitor the progress of the coagulation/flocculation process. Both pristine and functionalised CNTs demonstrated the ability to successfully coagulate colloidal particles in the brewery wastewater. Overall, ferric chloride was found to be a more effective coagulant than both the pristine and functionalised CNTshttp://www.elsevier.com/locate/watreshb2013ai201

A Review of Nanoparticles Toxicity and Their Routes of Exposures: Transdermal delivery of insulin

The new scientific innovation of engineering nanoparticles (NPs) at the atomic scale (diameter<100nm) has led to numerous novel and useful wide applications in electronics, chemicals, environmental protection, medical imaging, disease diagnoses, drug delivery, cancer treatment, gene therapy, etc.. The manufactures and consumers of the nanoparticles-related industrial products, however, are likely to be exposed to these engineered nanomaterials which have various physical and chemical properties at levels far beyond ambient concentrations. These nanosized particles are likely to increase unnecessary infinite toxicological effects on animals and environment; although their toxicological effects associated with human exposure are still unknown. To better understand the impact of these exposures on health, and how best to formulate appropriate monitoring and control strategies, this review seeks to examine various toxicological portal routes associated with NPs exposures. In fact, these ultrafine particles are capable of entering the body through skin pores, debilitated tissues, injection, olfactory, respiratory and intestinal tracts. These uptake routes of NPs may be intentional or unintentional. Their entry may lead tovarious diversified adverse biological effects. Until a clearer picture emerges, the limited data available suggest that caution must be exercised when potential exposures to NPs are encountered. Some methods have been used to determine the portal routes of nanoscale materials on experimental animals. They include pharyngeal instillation, injection, inhalation, cell culture lines and gavage exposures.This review also provides a step by step systematic approach for the easy identification and addressing of occupational health hazards arising from NPs

Removal of Pb2+ ions from synthetic wastewater using functionalized multi-walled carbon nanotubes decorated with green synthesized iron oxide–gold nanocomposite

Purification of wastewater before it is discharged into the aquatic environment is important in order to prevent pollution of clean water. This study investigated the applicability of functionalized multi-walled carbon nanotubes (MWCNTs) decorated with gold-iron oxide nanoparticles for the adsorptive removal of Pb2+ from synthetic wastewater. CNTs were commercially obtained and functionalized with a mixture of H2SO4/HNO3 acids. The CNTs were coated with gold-iron oxide nanoparticles, to enhance the adsorption of heavy metals. The gold-iron oxide nanoparticles were synthesized by reacting green tea leaf extract with iron chloride (FeCl2) and gold (III) chloride (HAuCl4) precursors. The composite was cross-linked using N, N-dimethylformadide (DMF). The adsorbents were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to assess their surface morphology, Fourier transform infrared (FTIR) spectroscopy to identify the functional groups present, X-ray diffraction (XRD) to ascertain the crystallographic structure of the green adsorbent and Raman spectroscopy to  determine the sample purity. SEM results showed highly agglomerated and polydispersed nanoparticles, owing to the presence of phytochemicals in the tea extract and magnetic interaction between the individual particles indicating the successful synthesis of Au/Fe3O4 adsorbent. Furthermore, an increase in the amount of Pb2+ removed per unit mass (qe) of adsorbent from 1.233 to 7.266 mg‧g-1 at 298 K was observed. A high sorption capacity was noticed for MWCNT-Au/Fe3O4 as compared to the MWCNT-COOH. The Pb2+ removal percentage increased from 50% to 78% with an increase in MWCNT-Au/Fe3O4 dosage from 0.02 g to 0.1 g. Adsorption isotherm data fitted well to the Freundlich and Langmuir isotherm models for MWCNT-COOH and MWCNT-Au/Fe3O4 adsorbents and the rate of Pb(II) adsorption by MWCNT-Au/Fe3O4 encountered an increase with increasing solution temperature and followed the pseudo-second-order model. The synthesized MWCNT-Au/Fe3O4 has good potential in removing heavy metals from wastewater

Adsorptive removal of BTEX compounds from wastewater using activated carbon derived from macadamia nut shells

In this study, adsorptive removal of benzene, toluene, ethylbenzene and xylenes (BTEX) from synthetic water using activated carbon adsorbent derived from macadamia nut shells was investigated. The surface functional groups of the synthesized adsorbents were assessed by Fourier transform infrared spectra. The specific surface area, pore size and pore volume at 77 K nitrogen adsorption, surface morphology, and the crystalline structure of the adsorbents were determined using Brunauer-Emmett-Teller, scanning electron microscopy and x-ray diffraction, respectively. Batch adsorption mode was used to evaluate the performance of the activated carbon.  The stock solutions of synthetic wastewater were prepared by dissolving 100 mg/L of each of the BTEX compound into distilled water in a 250 mL volumetric flask. Effect of initial concentration of BTEX compounds, contact time, and mass of adsorbent on the removal of BTEX compounds from the synthetic wastewater was investigated. The macadamia nut shell–derived activated carbon (MAC) proved to be an effective adsorbent for BTEX compounds, with a large surface area of 405.56 m2/g. The exposure time to reach equilibrium for maximum removal of BTEX was observed to be 20 min.  The adsorption capacity of the BTEX compounds by MAC followed the following adsorption order: benzene > toluene > ethylbenzene ˃ xylene

Synthesis of Poly-Alumino-Ferric Sulphate Coagulant from Acid Mine Drainage by Precipitation

The wastes generated from both operational and abandoned coal and metal mining are an environmental concern. These wastes, including acid mine drainage (AMD), are treated to abate the devastating effects they have on the environment before disposal. However, AMD contains valuable resources that can be recovered to subsidize treatment costs. Two of the major constituents of coal AMD are iron and aluminium, which can be recovered and engineered to function as coagulants. This work examines the potential of producing a poly-alumino-ferric sulphate (AMD-PAFS) coagulant from coal acidic drainage solutions. The co-precipitation of iron and aluminium is conducted at pH values of 5.0, 6.0 and 7.0 using sodium hydroxide in order to evaluate the recovery of iron and aluminium as hydroxide precipitates while minimizing the co-precipitation of the other heavy metals. The precipitation at pH 5.0 yields iron and aluminium recovery of 99.9 and 94.7%, respectively. An increase in the pH from 5.0 to 7.0 increases the recovery of aluminium to 99.1%, while the recovery of iron remains the same. The precipitate formed at pH 5.0 is used to produce a coagulant consisting of 89.5% and 10.0% iron and aluminium, respectively. The production of the coagulant is carried out by dissolving the precipitate in 5.0% (w/w) sulphuric acid. Subsequently, the treatment of the brewery wastewater shows that the AMD-PAFS coagulant is as efficient as the conventional poly ferric sulphate (PFS) coagulant. The turbidity removal is 91.9 and 87.8%, while the chemical oxygen demand (COD) removal is 56.0 and 64.0% for AMD-PAFS and PFS coagulants, respectively. The developed process, which can easily be incorporated into existing AMD treatment plants, not only reduces the sludge disposal problems but also creates revenue from waste

Ironmaking and Steelmaking Slags As Sustainable Adsorbents For Industrial Effluents And Wastewater Treatment:A critical review of properties, performance, challenges and opportunities

This paper critically discusses the structure, properties and applications of ironmaking and steelmaking slags and their silicate-based variants as low-cost adsorbents for removing cations and anions from industrial effluents and wastewater. Undoubtedly, the performance of slag-based adsorbents depends on their physical, chemical and phase chemical properties. The presence of crystalline phases, for example, has a significant effect on the adsorption capacity. However, despite their low cost and ubiquity, their chemical and geometric heterogeneity significantly affects the performance and applications of slag-based adsorbents. These challenges notwithstanding, the efficacy of slag-based adsorbents can be significantly enhanced through purposeful activation to increase the specific surface area and density of adsorption sites on the surfaces of adsorbent particles. The synthesis of functionalised adsorbents such as geopolymers, zeolites and layered double hydroxides from silicate and aluminosilicate precursors can also significantly increase the performance of slag-based adsorbents. In addition, the ability to stabilise the dissolved and/or entrained toxic metal species in stable phases in slags, either through controlled post-process fluxing or crystallisation, can significantly enhance the environmental performance of slag-based adsorbents. Most critical in the design of future slag-based adsorbents is the integration of the engineered properties of molten and solidified slags to the recovery and stabilisation of dissolved and/or entrained metals