Ion exchange of sodium chloride and sodium bicarbonate solutions using strong acid cation resins in relation to coal seam water treatment

Coal seam gas production has resulted in the production of large volumes of associated water which contains dissolved salts dominated by sodium chloride and sodium bicarbonate. Ion exchange using synthetic resins has been proposed as a method for desalination of coal seam water to make it suitable for various beneficial reuse options. This study investigated the behaviour of solutions of sodium chloride and sodium bicarbonate with respect to exchange with Lanxess S108H strong acid cation (SAC) resin. Equilibrium isotherms were created for solutions of NaCl and NaHCO3 and an actual sample of coal seam water from the Surat Basin in southern Queensland. The exchange of sodium ions arising from sodium bicarbonate was found to be considerably more favourable than exchange of sodium ions from sodium chloride solutions. This latter behaviour was attributed to the secondary decomposition of bicarbonate species under acidic conditions which resulted in the evolution of carbon dioxide and formation of water. The isotherm profiles could not be satisfactorily fitted by a single isotherm model such as the Langmuir expression. Instead, two Langmuir equations had to be simultaneously applied in order to fit the sections of the isotherm attributable to sodium ion exchange from sodium bicarbonate and sodium chloride. The shape of the isotherm profile was dependent upon the ratio of sodium chloride to sodium bicarbonate in solution and there was a high degree of correlation between simulated and actual coal seam water solutions

Comprehensive examination of acid leaching behaviour of mineral phases from red mud: Recovery of Fe, Al, Ti, and Si

Red mud represents an environmental and economic liability for the alumina industry in the form of wasted raw material. Although some leaching studies have been performed, there are deficiencies in the current literature regarding the amounts of metals extracted relative to each other, and minimal information regarding silicon contamination of extracts. There is also limited knowledge of extraction efficiencies of different acids (particularly in the case of phosphoric acid) under the same experimental conditions. This study focused on the leaching behaviour of the four most extractable elements present within red mud (iron, titanium, aluminium and silicon). By varying the experimental conditions, acid concentration, and type of acid, a comprehensive dataset of leaching trends was obtained. This allowed for direct comparison of leaching efficiency for the four elements under the same conditions, which was difficult previously due to the variation of experimental conditions and red mud composition between studies. The patterns in recoveries were explained in terms of the reactivities of the mineral phases within red mud and the interaction between the different acids and the reaction surfaces. Out of the four acids studied (nitric, hydrochloric, sulfuric, and phosphoric) phosphoric and hydrochloric acids produced some of the best recoveries for iron (76–78%) and titanium (23–24%), and phosphoric acid also produced the highest recoveries for silicon (49%) and aluminium (50%). The differences observed between the acid types and reaction conditions revealed potential for development of element selective extraction methods.\ud Additionally, explaining leaching behaviour in terms of the mineral phases present allowed easier prediction of expected leaching trends for these four elements, which made this study applicable to red muds with a wide variety of compositions

Enhanced removal of Mn (II) from solution by thermally activated Bayer precipitates

This study assessed the ability of thermally activated Bayer precipitates (Bppt) for manganese remediation from acidic solutions, focusing on their application in acid mine drainage water. The Bayer precipitates were formed from the addition of seawater to Bayer liquor residues, and were primarily composed of hydrotalcite and calcium carbonate. Thermal activation of these materials at 320, 380 and 440 °C showed a reduction in Bayer hydrotalcite crystallinity and increased surface area due to the decarbonation and dehydroxylation of the mixed metal hydroxide layers in Bayer hydrotalcite. At higher thermal activation temperatures (380 and 440 °C), partial decarbonation of calcium carbonate were suspected of forming calcium oxide, which aided the neutralisation process. The removal capacities for manganese were found to increase with thermal activation temperature, which corresponded with increased maximum pH (pH > 10 for 380 and 440 °C heated sample). Treatment of acidic solutions with Bayer precipitates simultaneously removed manganese and aluminium, which is not achievable in lime neutralisation technologies currently used in acid mine drainage treatment. The optimum thermal activation temperature was found to be 380 °C, showing high manganese removal performance and a ten-fold reduction in material mass required when compared to Bayer precipitate. Removal mechanisms of manganese were found to be a combination of hydrotalcite reformation (determined by X-ray photoelectron spectroscopy, X-ray diffraction and infrared spectroscopy), surface precipitation and surface complexation, as well as the formation of hausmannite and rhodochrosite.</p

Behaviour of natural zeolites used for the treatment of simulated and actual coal seam gas water

Coal seam gas operations produce significant quantities of associated water which often require demineralization. Ion exchange with natural zeolites has been proposed as a possible approach. The interaction of natural zeolites with solutions of sodium chloride and sodium bicarbonate in addition to coal seam gas water is not clear. Hence, we investigated ion exchange kinetics, equilibrium, and column behaviour of an Australian natural zeolite. Kinetic tests suggested that the pseudo first order equation best simulated the data. Intraparticle diffusion was part of the rate limiting step and more than one diffusion process controlled the overall rate of sodium ion uptake. Using a constant mass of zeolite and variable concentration of either sodium chloride or sodium bicarbonate resulted in a convex isotherm which was fitted by a Langmuir model. However, using a variable mass of zeolite and constant concentration of sodium ions revealed that the exchange of sodium ions with the zeolite surface sites was in fact unfavourable. Sodium ion exchange from bicarbonate solutions (10.3 g Na/kg zeolite) was preferred relative to exchange from sodium chloride solutions (6.4 g Na/kg zeolite). The formation of calcium carbonate species was proposed to explain the observed behaviour. Column studies of coal seam gas water showed that natural zeolite had limited ability to reduce the concentration of sodium ions (loading 2.1 g Na/kg zeolite) with rapid breakthrough observed. It was concluded that natural zeolites may not be suitable for the removal of cations from coal seam gas water without improvement of their physical properties

Ferrous poisoning of surface MnO2 during manganese greensand operation

This study investigated the fundamental performance of manganese greensands for the removal of both dissolved manganese and iron species from solution. The hypothesis was that iron ions may detrimentally impact manganese removal and that the magnitude of this outcome was dependent upon greensand composition. Consequently, five greensand materials were examined in terms of repeatability of operation, the relationship of performance to physical criteria, the mechanism of removal, influence of solution pH and the performance changes that occur when manganese and iron were co-present in solution.\ud \ud All greensand medias were shown to remove Mn(II) over 5 treatment cycles, where the solid MnO2 media had a larger removal capacity (0.35 mg/g) compared to the two coated medias (0.09 and 0.05 mg/g, respectively). The greensand medias also showed a significant capacity reduction from 72 to 93% when Fe(II) containing solutions were examined. Fe(II) species were also found to leach considerable amounts of Mn(II) through reductive dissolution which negated the beneficial Mn(II) removal when treating solutions with co-present Fe(II) and Mn(II). Material characterization revealed that the Mn(II) removal mechanism did not involve any surface MnO2 phase change or rely solely on Mn(II) adsorption

Critical evaluation of zeolite N synthesis parameters which influence process design

Zeolite N exhibits high selectivity and capacity for ammonium ions, which makes it attractive applications such as wastewater treatment. However, there is a lack of knowledge regarding process issues pertinent to zeolite synthesis scale-up. Therefore, this study addressed factors including agitation of reactant solution during zeolite N synthesis, the benefit of mother liquor recycling, zeolite washing strategies, influence of clay source, reactor geometry and materials of construction. Use of both stirred and static reactant solutions did not impact the rate of zeolite N formation when the reaction temperature was 120 oC; whereas at 100 oC stirring promoted the creation of zeolite N. Stirred solutions resulted in smaller zeolite crystals. Mother liquor recycling not only reduced the need for KOH and KCl but also enhanced the product quality (cation exchange capacity increased from 558 to 586 meq/100 g). Reuse of the first stage wash water was recommended as it comprised of a comparable potassium content as the mother liquor (c.f. 13.1-15.4 g, respectively). Addition of acid or salts to the wash water did not remarkably accelerate the reduction in effluent solution pH. Excessive quartz content in the clay feedstock inhibited the growth of zeolite N. It was necessary to adjust the SiO2/Al2O3 feed ratio to 2 by pre-dissolving Al(OH)3 in potassium hydroxide. Use of two different reactor types to make zeolite N suggested that reaction time was significantly faster if reactors were made of Inconel (4 h) and did not contain a teflon insert (8 h).</p

Ammoniacal nitrogen removal and reuse : Process engineering design and technoeconomics of zeolite N synthesis

This investigation of Zeolite N synthesis addressed process flow design and manufacturing economics. Zeolite N is important as it has high selectivity and capacity for ammonium ions which means it has applications in wastewater treatment or nutrient management. The aim was to accelerate zeolite N use by developing an optimal economic model for zeolite N synthesis. Three process designs for 30 tonnes per day zeolite N production were evaluated; (1) No recycling of mother liquor or wash water; (2) recycling of mother liquor; (3) recycling of mother liquor and wash water. Recycling strategies reduced demand for KOH &amp; KCl by 58% and 83%, respectively. Water consumption was lowest for the mother liquor/wash water recycling plant (c.f. 185 m3 per batch compared to 290 m3 per batch for base case). Similarly, wastewater generation was least when using the mother liquor/wash water recycling approach. Capital expenditure was similar for the three processes (A$14,190,750 to A$15,504,000). However, operational expenditure was considerably less when recycling mother liquor and wash water. The highest net present value (NPV) for zeolite N synthesis resulted from internal recycling of mother liquor and first stage wash water (A$85,813,532) resulting in a payback period of 2.44 years. Notably the assumed zeolite N selling price of A$2000 per tonne was less than the literature value of A$3067 per tonne which was suggested to be economically attractive. Sensitivity analysis indicated a break-even point of A$1300 per tonne of zeolite N and that zeolite price was the major factor controlling project viability. </p

Settling behaviours of low alumina/caustic ratios during seawater neutralisation of Bayer liquor

Factors that affect the settleability of seawater neutralised bauxite refinery residues are poorly understood, in particular, the settleability of precipitates in the absence of red mud and those formed with different alumina/caustic (AC) ratios. The influence of temperature, AC ratio, caustic concentration and the volumetric ratio of seawater on the settleability of seawater neutralisation precipitates and their respective compositions and stabilities have been determined. An array of techniques have been used to determine the composition and stability of precipitates and include pH, conductivity, inductively coupled plasma optical emission spectroscopy, infrared spectroscopy and X-ray diffraction. Temperature has been shown to have a significant influence on the settleability and calcium carbonate phase distributions in precipitates, as well as the overall stability of the precipitates. More complex phase compositions have also been found for Bayer liquors with lower AC ratios. The caustic concentration and temperature of the reaction have the greatest influence on the settling efficiency of the precipitates. Assessments on the chemical stability of the precipitates, precipitate settleability and discharge water quality have been made. In addition, productivity and environmental impacts caused by changes in precipitate settleability have also been considered

Application of non-linear regression analysis and statistical testing to equilibrium isotherms:Building an Excel template and interpretation

This study developed a Microsoft Excel based spreadsheet which acted as a template for researchers to construct sorption equilibrium isotherms and apply equilibrium non-linear models to the experimental data. The spreadsheet also incorporated uncertainty estimators, such as standard error and 95% confidence intervals (CI), as well as goodness-of-fit metrics, such as R2 and F-test. Insights into the effects of isotherm experimental design and repeats were discussed. The 95% CI metric applied was an acceptable metric for the uncertainty associated with the loading capacity, qmax. The F-test was demonstrated to be an appropriate goodness-of-fit metric, which assessed the probability that the variance of the model and experimental data was the same. The importance of appropriate equipment selection and experimental design with respect to isotherm interpretation was highlighted. The spreadsheet was made available for the benefit of all researchers to use.</p