In order to increase the current efficiency in copper electrowinning tankhouses, iron can be removed from the electrolyte using ion exchange. While this is a proven technology, very little data is available for the application of this technology to copper electrowinning electrolytes containing antimony and bismuth. The feasibility of utilizing iron ion exchange for the removal of iron from copper electrowinning electrolytes containing antimony and bismuth was studied in the laboratory. Apicolylamine, a sulphonated diphosphonic, an aminophosphonic and three sulphonated monophosphonic resins were tested. The picolylamine resin was found to be completely impractical as it loaded high levels of copper. All the phosphonic resins tested loaded an appreciable amount of antimony, however, only the aminophosponic resin loaded an appreciable amount of bismuth. Tests to determine whether or not the sulphonated monophosphonic Purolite S957 resin would continue to load antimony with time and, hence, reduce the resin's ability to remove iron gave inconclusive results. In the event that the resin's ability to remove iron is hampered due to antimony loading, testing has shown that the resin performance may be restored via a regeneration with a solution containing sulphuric acid and sodium chloride. A case study for the application of this technology to the CVRD Inco CRED plant has shown that, while iron removal by ion exchange is technically feasible, it will upset the plant's acid balance in electrolyte. Therefore, an acid removal process would need to be implemented in tandem with an iron ion exchange system. Additionally, preliminary calculations suggest that a system with a single ion exchange column may have difficulty removing sufficient iron for the CRED design conditions. Therefore, consideration should be given to the possibility of utilizing a two column system (one column loading, one column stripping).

As one of the most abundant elements on earth, iron is nearly always present in metal concentrates. This is specifically true for zinc sulphide concentrates, which can contain up to 18% iron (marmatite). Today more than half of these concentrates are treated in hydrometallurgical- or combined hydrometallurgical¬pyrometallurgical circuits. In hydrometallurgical circuits, iron is solubilised (either in a roast-Ieach-, a direct leach- or bacterial leach circuit) along with zinc and must be removed from the zinc¬rich solution before the electrowinning- or solvent extraction step. Various iron removal processes were developed to address the iron problem in hydrometallurgical circuits. The better known of these include the jarosite-, goethite- and hematite processes also used in the zinc industry. Zincor (Zinc Corporation of South Africa) patented an iron removal process (Zincor Process), which was generally considered to be very similar to the so-called "para-goethite" iron removal process used only in two other zinc smelters notably Porto Vesme (Italy) and Pasminco Hobart (Tasmania). However, since the Zincor Process was patented in 1976, various changes have been made such as a change from a batch parallel to a continuous series process, a change in precipitation pH-profile and the introduction of a pH controlled acid wash in the second tank. The introduction of a weak acid leach step and vacuum belt filters at Zincor's residue treatment plant in the near future and an iron removal process that is not clearly understood, necessitated this further study of the Zincor iron removal process. The study has been conducted in three parts. The first part of the study has focused on the characterisation of the Zincor iron residue and the Zincor process. The second part of the study has been concerned with the definition of an optimum operating window in terms of the filterability of the residue and the third part investigated the use of neutralisation reagents other than zinc calcine to control the pH during iron precipitation. The distribution of iron in the Zincor iron precipitate, which usually contains between 35% and 40% iron, has been found to be as follows: approximately 45% as schwertmannite, 5% as ferrihydrite, 20% as jarosites, 25% as franklinite, trace amounts of pyrite as well as 5% of an unknown phase. This confirmed that goethite is not present in the Zincor iron residue and that iron is mainly removed in the form of amorphous intermediate iron phases such as schwertmannite and ferrihydrite. Of these two phases, schwertmannite was the least expected as most work up until now were done on samples taken from natural environments. The following description of the conditions that promote iron removal, mainly as schwertmannite, is viewed as an expansion of the available literature data, which was gathered at ambient conditions. In terms of the main operating parameters, optimum filterability was achieved under the following conditions: pH of 3.0, temperature as high as possible (70°C) and at least 25 kg/m3 seeding. A retention time of at least 4 hours at a pH of 3.0 and 60°C was required, which decreased by more than 50% at a temperature of 70°C. As these conditions mainly impact on the soluble zinc loss encountered during iron removal, an effort was made to further reduce the insoluble zinc loss, which is the inherent weakness in the Zincor process, and similar processes where zinc calcine is used for pH control, by investigating the use of alternative neutralisation reagents. This study showed that iron can be successfully removed with Ca(OH) 2, a basic zinc sulphate and zinc oxide mixture as well as chemically precipitated CaC03 produced in the paper and pulp industry. Of these alternatives, CaC03 appeared to be the most promising, with filtration rates an order of magnitude higher than the zinc oxide options (calcine and basic zinc sulphate mixture), due to better overall economics than with the use of Ca(OH) 2. Utilisation CaC03 as an alternative neutralisation agent might increase the overall zinc recovery figure at Zincor by up to 1.5%. Based on the findings, it can be concluded that the Zincor process in its current form has a very distinct character compared to what was historically considered to be the very similar patented para-goethite iron removal process, as practiced at the Porto Vesme and the Pasminco Hobart hydrometallurgical zinc plants. / Dissertation (MEng (Metallurgical Engineering))--University of Pretoria, 2006. / Materials Science and Metallurgical Engineering / unrestricted

No description available.

The presence of naturally occurring arsenic in groundwater has caused a number of social and health-related problems for the rural poor of Bangladesh. Today, it is estimated that 42 – 60 million people in Bangladesh consume water at arsenic concentrations greater than the World Health Organization (WHO) standard of 10 μg/L. The arsenic-iron removal plant (AIRP) has been widely used to remove arsenic from drinking water across much of the country; however, AIRPs show variable levels of efficiency and have often failed to meet the WHO standard. Those who continue to drink water with elevated concentrations of arsenic are prone to skin disease and various cancers. The thesis presented here examines methods to mitigate exposure of the rural poor to arsenic by modifying the AIRP and increasing our understanding of the chemical and social factors associated with its use. This objective is accomplished via four channels: (1) assessment of the chemical processes occurring within the AIRP, (2) evaluation of three retrofits, (3) development of a waste management strategy, and (4) examination of social factors affecting use and sustainability of the AIRP. Household AIRPs installed in the village of Mohadevpur, in the Manikganj district, are examined.

No description available.

This dissertation reports the design of a process (patent pending) to remove iron from acid mine drainage (AMD) without the formation of metal hydroxide sludge. The system includes the oxidation of ferrous iron in a packed bed bioreactor, the precipitation of iron within a fluidized bed, the removal of manganese and heavy metals (Cu, Ni, Zn) in a trickling filter at high (>9) pH, with final neutralization in a carbonate bed. The technique avoided the generation of iron oxyhydroxide sludge. In the packed bed bioreactor, maximum substrate oxidation rate (R_,max) was 1500 mg L⁻¹ h⁻¹ at dilution rates of 2 h⁻¹, with oxidation efficiency at 98%. The half-saturation constant (similar to a Ks) was 6 mg L⁻¹. The oxidation rate was affected by dissolved oxygen below 2 mg L⁻¹, with a Monod-type Ko for DO of 0.33 mg L⁻¹. Temperature had a significant effect on oxidation rate, but pH (2.0 to 3.25) and supplemental CO₂ did not affect oxidation rates. Iron hydroxide precipitation was not instantaneous when base was added at a OH/Fe ratio of less than 3. Induction time was found to be a function of pH, sulfate concentration and iron concentration, with a multiple R² of 0.84. Aqueous [Al (III)] and [Mn (II)] did not significantly (α = 0.05) affect induction time over the range of concentrations investigated. When specific loading to the fluidized bed reactor exceeded 0.20 mg Fe m⁻² h⁻¹, dispersed iron particulates formed leading to a turbid effluent. Reactor pH determined the minimum iron concentration in the effluent, with an optimal at pH 3.5. Total iron removals of 98% were achieved in the fluidized bed with effluent [Fe] below 10 mg L⁻¹. Further iron removal occurred within the calcium carbonate bed. Heavy metals were removed both in the fluidized bed reactor as well as in the trickling filter. Oxidation at pH >9 caused manganese to precipitate (96% removal); removals of copper, nickel, and zinc were due primarily to sorption onto oxide surfaces. Removals averaged 97% for copper, 70% for nickel and 94% for zinc. The treatment strategy produced an effluent relatively free of iron (< 3 mg/L), without the formation of iron sludge and may be suitable for AMD seeps, drainage from acidic tailings ponds, active mine effluent, and acidic iron-rich industrial wastewater. / Ph. D.

In this thesis, the implementation and results of studies into the effect of pH on the kinetics of various iron transformations in natural waters are described. Specific studies include i) the oxidation of Fe(II) in the absence and presence of both model and natural organic ligands, ii) the complexation of Fe(III) by model organic compounds, and iii) the precipitation of Fe(III) through the use of both laboratory investigations of iron species and kinetic modeling. In the absence of organic ligands, oxidation of nanomolar concentrations of Fe(II) over the pH range 6.0 -- 8.0 is predominantly controlled by the reaction of Fe(II) with oxygen and with superoxide while the disproportionation of superoxide appears to be negligible. Oxidation of Fe(II) by hydrogen peroxide, back reduction of Fe(III) by superoxide and precipitation of Fe(III) have been shown to exert some influences at various stages of the oxidation at different pH and initial Fe(II) concentrations. In the presence of organic ligands, different effects on the Fe(II) oxidation kinetics is shown with different organic ligands, their initial concentrations and with varying pH. A detailed kinetic model is developed and shown to adequately describe the kinetics of Fe(II) oxidation in the absence and presence of various ligands over a range of concentrations and pH. The applicability of the previous oxidation models to describe the experimental data is assessed. Rate constants for formation of Fe(III) by a range of model organic compounds over the pH range 6.0 -- 9.5 are determined. Variation of rate constants for Fe(III) complexation by desferrioxamine B and ethylenediaminetetraacetate with varying pH is explained by an outer-sphere complexation model. The significant variation in rate constants of Fe(III) complexation by salicylate, 5-sulfosalicylate, citrate and 3,4-dihydroxylbenzoate with varying pH is possibly due to the presence of different complexes at different pH. The results of this study demonstrate that organic ligands from different sources may influence the speciation of iron in vastly different ways. The kinetics of Fe(III) precipitation are investigated in bicarbonate solutions over the pH range 6.0 -- 9.5. The rate of precipitation varies by nearly two orders of magnitude with a maximum rate constant at a pH of around 8.0. The results of the study support the existence of the dissolved neutral species Fe(OH)30 and suggests that it is the dominant precursor in Fe(III) polymerization and subsequent precipitation at circumneutral pH. Variation in the precipitation rate constant over the pH range considered is consistent with a mechanism in which the kinetics of iron precipitation are controlled by rates of water exchange in dissolved iron hydrolysis species.

In this thesis, the implementation and results of studies into the effect of pH on the kinetics of various iron transformations in natural waters are described. Specific studies include i) the oxidation of Fe(II) in the absence and presence of both model and natural organic ligands, ii) the complexation of Fe(III) by model organic compounds, and iii) the precipitation of Fe(III) through the use of both laboratory investigations of iron species and kinetic modeling. In the absence of organic ligands, oxidation of nanomolar concentrations of Fe(II) over the pH range 6.0 -- 8.0 is predominantly controlled by the reaction of Fe(II) with oxygen and with superoxide while the disproportionation of superoxide appears to be negligible. Oxidation of Fe(II) by hydrogen peroxide, back reduction of Fe(III) by superoxide and precipitation of Fe(III) have been shown to exert some influences at various stages of the oxidation at different pH and initial Fe(II) concentrations. In the presence of organic ligands, different effects on the Fe(II) oxidation kinetics is shown with different organic ligands, their initial concentrations and with varying pH. A detailed kinetic model is developed and shown to adequately describe the kinetics of Fe(II) oxidation in the absence and presence of various ligands over a range of concentrations and pH. The applicability of the previous oxidation models to describe the experimental data is assessed. Rate constants for formation of Fe(III) by a range of model organic compounds over the pH range 6.0 -- 9.5 are determined. Variation of rate constants for Fe(III) complexation by desferrioxamine B and ethylenediaminetetraacetate with varying pH is explained by an outer-sphere complexation model. The significant variation in rate constants of Fe(III) complexation by salicylate, 5-sulfosalicylate, citrate and 3,4-dihydroxylbenzoate with varying pH is possibly due to the presence of different complexes at different pH. The results of this study demonstrate that organic ligands from different sources may influence the speciation of iron in vastly different ways. The kinetics of Fe(III) precipitation are investigated in bicarbonate solutions over the pH range 6.0 -- 9.5. The rate of precipitation varies by nearly two orders of magnitude with a maximum rate constant at a pH of around 8.0. The results of the study support the existence of the dissolved neutral species Fe(OH)30 and suggests that it is the dominant precursor in Fe(III) polymerization and subsequent precipitation at circumneutral pH. Variation in the precipitation rate constant over the pH range considered is consistent with a mechanism in which the kinetics of iron precipitation are controlled by rates of water exchange in dissolved iron hydrolysis species.

This study evaluated alternatives to continuously regenerated greensand for iron and manganese removal. Specific objectives were (1) to investigate the applicability for removing soluble manganese by adsorption and oxidation onto the surface of manganese oxide-coated media, and (2) to develop mathematical models to predict the removal of soluble manganese both in the presence and absence of free chlorine. Results from a pilot-scale experiment in Columbus, Indiana, showed that when the filters were operated in a conventional oxidant addition mode (i.e., with the addition of HOCI and KMnO₄) the anthracite-sand and anthracite-sand-garnet configurations both provided efficient treatment because of the reduced rate of head loss. Further experiments, without the use of KMnO₄ or greensand, equally removed manganese by adsorption and oxidation onto oxide-coated media; however, the treatment process resulted in reduced head loss and oxidant costs. Results from this study and other previous research demonstrated that manganese removal by oxide coatings is an efficient and functional treatment mechanism. However, little quantitative information was available to predict these processes. Therefore, mathematical models were developed to help predict design and operational conditions needed to implement oxide-coated media as a treatment process. Two separate models were developed to predict (1) the continuous removal of soluble manganese in the presence of free chlorine (continuous regeneration model), and (2) the eventual breakthrough of soluble manganese without oxidant addition (intermittent regeneration model). Each model was derived from chemical reaction, mass balance, or isotherm equations and was further developed by a sensitivity analysis and parameter estimation. The two models were then verified by predicting manganese removal from independent research. The continuous regeneration model can help predict the removal of soluble manganese by adsorption and oxidation on the surface of oxide-coated media and is useful in the design of filters for continuous Mn(Il) removal. The intermittent regeneration model effectively predicts the performance of filters without the addition of an oxidant and is useful for treatment plants which cannot apply chlorine continuously to their filter applied water. / Master of Science

The fate of iron complexed by various organic compounds was investigated as a function of both chemical oxidative and coagulation removal methods. Dissolved organic carbon (DOC) utilized in the studies was obtained from a variety of sources and included humic and fulvic acids, tannic acid and oxalic acid. Oxidants evaluated were potassium permanganate, free chlorine, and chlorine dioxide. Both laboratory-scale and field monitoring studies were performed. The relative molecular weight distribution (MWD) of the DOC present was analyzed to evaluate how changes in this parameter affected the efficiency of soluble iron removal by oxidation. In addition, the MWD of selected coagulated samples was evaluated to determine how this parameter affected the fate of complexed iron during the coagulation of dissolved organic matter with alum. A high degree of ferrous iron complexation occurred with the DOC dominated by higher molecular weight organics. This complexation rendered the iron stable against the addition of each of the oxidants evaluated. However, soluble Fe(II) complexed by low molecular weight organics was successfully removed by chemical oxidation. Potassium permanganate was found to be the most effective oxidant of the three oxidants utilized in the study. The results indicated that soluble Fe(II) complexed by high molecular weight DOC can be efficiently removed by alum coagulation. The pH and alum dose utilized to produce effective DOC removal was also found to promote efficient complexed Fe(II) removal. / Master of Science