Process Liquors Research Articles

Environmental profile of textile wet processing in Finland

This study was carried out in major Finnish textile companies in order to create an environmental impact profile for wet processing in Finland as a part of drafting the Best Available Technique (BAT) Reference documents for the European IPPC Bureau. System boundaries were defined for alternative process technologies to be used in BAT definitions. The use of resources and process emissions is, however, monitored for the whole wet processing only in the companies under study. No remarkable differences in energy and water consumption between continuous and batch wet processing could be measured; the lowest dyeing liquor ratios were reported on jet machines and the highest on winch dyeing machines. Dyestuff consumption depends on the colour shade required; some dyes have, however, low fixation rates, such as reactive and sulphur dyes, only 60% on average. About 20% of the process liquor containing unfixed dyestuffs and auxiliaries end up in sewage treatment plants. These chemicals are not recovered and reused in the companies under study. All industrial plants in Finland discharge their wastewater to municipal sewage treatment plants, which carry out wastewater analysis and control. All textile plants, which use more than 50 tonnes of organic solvents per year, are under official off-gas control in Finland.

Removal of Chloride and Potassium from Kraft Chemical Recovery Cycles

The current paper shows how a system for removal of both chloride and potassium may be incorporated in a potential future kraft chemical recovery system, where the traditional recovery boiler has been replaced by a black liquor gasifier. The suggested process involves cooling crystallization of sodium carbonate and sodium bicarbonate from a preferentially sulfide lean green liquor, leaving a stream depleted of useful chemicals but rich in chloride and potassium, that may be led to sewer. The investigation includes a modeling part, where a thermodynamic model has been used to calculate the solubility limits in the green liquor, and an experimental part, where both synthetic green liquor (with a controlled composition) and green liquor taken from a Swedish mill were used. The results show that the suggested process functions well and that both chloride and potassium will be selectively removed from the green liquor, while the useful chemicals will be recovered for reuse in the pulp mill. The size of the system necessary for the suggested process will depend on the concentrations of chloride and potassium that can be tolerated in the process liquor—an example is given showing the technical feasibility of the suggested process.

Analytical options for control of acids and bases in hydrometallurgical processes

The most common procedures for the determination of acids and bases in hydrometallurgical process liquors are reviewed and compared. Automated batch titrations, performed by stepwise addition of titrant and using Gran plots for evaluation are reliable but slow compared to flow techniques. Continuous flow titrations are grouped into three classes: Flow Injection Titration, Single Point Flow Injection Titration, and Triangle-programmed Flow Titrations. Furthermore, Sequential Injection Analysis is also considered for process applications. Each one of these methods has advantages and drawbacks. An overview of the most common application problems, and the way they are solved with each methodology, is given. The analytical characteristics of the described procedures are given as well as a guide for the choice of technique for a given application.

Liquid–liquid extraction of gallium from Bayer process liquor using Kelex 100 in the presence of surfactants

The solvent extraction of gallium from a concentrated Bayer process liquor containing ≃450 g/l of Na 2O, ≃80 g/l of Al 2O 3 and 190±20 ppm of gallium was investigated using 12 vol.% Kelex 100, a 7-alkyl substituted-8 hydroxyquinoline as extractant, 12 vol.% isodecanol as modifier and kerosene as diluent. At 1.0:1.0 organic to aqueous phase ratio and at room temperature, 80% of gallium was recovered in 3 h. In order to improve upon the kinetics of extraction, the addition of surfactants in the organic phase was studied. The addition of octylamine to the organic phase was found to reduce the rate of gallium extraction as well as its recovery. Additions of petroleum sulphonate up to 0.5 vol.% of organic phase has increased the rate of gallium extraction by reducing the equilibrium time to 45 min along with 80% recovery of gallium. When the petroleum sulphonate addition was increased to 2.5 vol.%, the rate of extraction and the recovery decreased significantly. The Versatic 10 volume percentage was studied at 1.0, 2.5, 5.0 and 10 by adjusting the kerosene volume percentage. Gradual increase in the volume percentage of Versatic 10 resulted in a decrease in the equilibrium time, and the maximum recovery of 98% of gallium was obtained at 2.5 vol.% Versatic 10 in 15 min. With further increase in the Versatic 10 volume percentage, the gallium recovery was decreased.

The dissolution of iron in the hydrochloric acid leach of an ilmenite concentrate

Hydrochloric acid leach processes for upgrading ilmenite to synthetic rutile are being considered for use with the Australian ilmenite concentrates that cannot be treated by the commonly used Becher process. These acid leach processes consist of a pre-leach thermal treatment, a hydrochloric acid leach that extracts iron from the concentrate, and a regeneration step that forms hydrochloric acid from the ferrous chloride produced in the leach. The acid leach processes differ in their thermal pre-treatments, but common to them all is a leach at temperatures near the boiling point of the acid. The present investigation of the acid leach step, applied to a Western Australian ilmenite concentrate, clarifies the chemical processes that occur in the leach and, through a designed experiment, identifies factors that affect the rate of extraction of iron. The four controlled variables studied were: the concentrations of ethanol, hydrochloric acid, and ferrous chloride in the leach liquor, and the quantity of oxygen injected into the liquor. The extraction of iron was shown to occur in two stages: an initially rapid dissolution of iron, decomposing the 45% Fe 2O 3 ilmenite into an impure rutile containing 0.42% to 0.65% Fe 2O 3; and a slower dissolution of this iron out of the rutile. This initially rapid rate of iron extraction is altered by process liquor conditions. Thus, it is reduced by ethanol addition, and increased in more concentrated acid. It is also increased by ferrous chloride addition, up to an optimum concentration (determined by the acid concentration), but decreased by its further addition.

Removal of Heavy Metals and Lanthanides from Industrial Phosphoric Acid Process Liquors

To diminish the discharge of heavy metals and lanthanides by the phosphoric acid industry, these impurities have to be removed from the mother liquor before their incorporation in the gypsum crystals. This can best be achieved by means of solvent extraction or ion exchange during the recrystallization of hemihydrate to dihydrate gypsum. Various commercial carriers and two ion-exchange resins were screened for their efficiency and selectivity. Light and heavy lanthanide ions are extracted from the recrystallization acid by didodecylnaphthalenesulfonic acid (Nacure 1052) and di-(2-ethylhexyl)phosphoric acid (D2EHPA), and the heavy-metal ions by bis(2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex 301) and by bis(2,4,4-trimethylpentyl)monothiophosphinic acid (Cyanex 302). Mercury is also extracted by the anion carriers tri(C8–C10)amine (Alamine 336) and tri(C8–C10) monomethyl ammonium chloride (Aliquat 336). Both Dowex C-500 and Amberlite IR-120 extract lanthanide and heavy-metal ions. Unfortunately, D2EHPA, Nacure 1052, and the two ion-exchange resins also show affinity for ions present in much higher concentrations, like calcium or iron ions.

Determining silica solubility in bayer process liquor

The efficient precipitation of dissolved silica from Bayer process liquor is essential for the production of high-quality alumina and the reduction of excessive scaling in the heat exchangers in the evaporation building of Bayer processes. The accurate prediction of silica solubility in Bayer liquor is one of the key parameters in improving the design and operation of the desilication process. Previous findings, particularly with respect to the influence of temperature and concentrations of caustic soda and alumina on the solubility of silica, are inconclusive. In this article, experimental results are presented over a wide range of temperature and alumina and caustic soda concentrations. Attempts are made to utilize artificial neural networks for identifying the process variables and modeling. The radial basis function neural network architecture was used successfully to generate a nonlinear correlation for the prediction of the solubility of silica in Bayer process liquor. The resulting correlation can predict the present data and the control data of other investigators with good accuracy.

Comparison of Bauxite and Bayer Liquor Humic Substances by 13C Nuclear Magnetic Resonance Spectroscopy. Implications for the Fate of Humic Substances in the Bayer Process

Solid-state 13C nuclear magnetic resonance (NMR) spectra of humic substances extracted from bauxite and Bayer Process liquor have been recorded. Relative to the bauxite humics, the Bayer liquor humics contain less aliphatic and carboxyl carbon and more aromatic carbon. There are corresponding differences in elemental H:C and O:C ratios. However, the liquor fulvic acid proved to have a greater titratable acidity than bauxite fulvic acid, probably as a result of a combination of oxidation processes on the humic macromolecules. The behavior of simple carboxylic acids under Bayer Process-like conditions indicated similar stabilities, with aliphatic compounds being destroyed and aromatic compounds being more stable. The cyclical nature of the process allows the aromatic-rich humics to achieve gram per liter concentrations in the liquor.

Spectrophotometric in-line monitoring of the electrochemical production of polysulfides using an ATR-probe

With an ATR-probe For the UV-vis range it is possible to apply spectrophotometry to very concentrated process liquors without dilution. In this paper the application of a new ATR-probe to the monit ...

Transfer, pathways, enrichment and discharge of trace elements in the pulp industry measured by means of neutron activation analysis

In Norway trace elements are transferred from terrestrial ecosystems to coastal sea water via the forest industry. Raw materials (wood, bark and freshwater) contain relatively low concentrations of trace elements, but due to the high volume, processed wood and bark are the main sources of element input to the industrial pulp production process. Up to 80% of the elements enter the pulp process via wood. Thus, the annual flux of trace elements can be regarded as substantial. The purpose of this investigation is to study transfer, redistribution, enrichment and discharges of trace elements from the pulp industry. Instrumental neutron activation analysis (INAA), is used to determine the concentrations of Cd, Ce, Co, Cs, Eu, Fe, La, Rb, Sc, Sm, Sr and Zn in samples of the different raw materials, process liquors, waste and waste water and products from processing. Lead, Cu and Ni were measured by means of atomic absorption spectroscopy with graphite furnace (GFAAS) and inductive coupled plasma atomic emission spectroscopy (ICP-AES). Recycling of chemicals leads to enrichment of trace elements. Corrosion of tubes and tanks gives increased concentration of Pb, Cu and transition elements in the re-cycling circles. For all other elements the process reaches a `steady state'; hence the annual input is equal to the annual output (kg/year). The products contained very low levels of trace elements. For all the trace elements<20% of the total output from the process and for some elements only 5%, were found in the products. Discharges of trace elements from the investigated pulp production plant to the fjord reached 70% of the annual trace element output in 1993 while the remaining fraction was stored as waste.

Reactions of lime with carbonate-containing solutions

In the Bayer process for refining alumina, lime (either quicklime or slaked lime) is added to the process liquor to precipitate calcium carbonate and restore alkalinity to the solution. The work described in this paper was undertaken to elucidate the mechanism of this precipitation reaction about which surprisingly little is known. In the first part of the study, the composition of calcium oxide disks after reacting with sodium carbonate solutions was examined by XRD and TGA. TGA results show that the amount of calcium carbonate formed on the disks increases with sodium carbonate concentration but the amount of calcium hydroxide reaches a minimum at a solution concentration of about 0.05 M carbonate and then increases at higher carbonate concentrations. The kinetics of the formation of calcium carbonate were also followed using HPLC to monitor the change in bulk carbonate concentration due to the reaction of powdered lime in sodium carbonate solutions. The effect of the agitation speed and temperature on the reaction rate indicates that the formation of calcium carbonate is a diffusion-controlled process. To account for these findings it is suggested that at concentrations above 0.05 M carbonate a more porous heterogeneous CaCO 3–Ca(OH) 2 layer appears owing to direct attack on the surface by carbonate before a layer of calcium hydroxide can form. Scanning electron micrographs of disks after reaction in carbonate solutions support this suggestion. The second part of this study deals with the dissolution of lime in the presence of sodium carbonate. The concentration of Ca 2+ from dissolution of calcium hydroxide disks was determined by AAS. It was found that the dissolution process is slowed by the formation of calcium carbonate, and is diffusion controlled. The reaction of powdered calcium oxide in the sodium carbonate solution was followed by calorimetry. It was found that the relationship between the extent of dissolution and the carbonate concentration is similar to that obtained by TGA for the formation of calcium carbonate, suggesting the same mechanism.

Photochemical decomposition of trisoxalatoiron(III): A hydrometallurgical application of daylight

As part of a study of oxalic acid leaching to reduce the iron content of glass sand, photochemical reduction of trisoxalatoiron(III) species formed in the leachates and precipitation of the product as iron(II) oxalate dihydrate were examined as potential means of treating process liquors. Parametric studies showed that, under favourable conditions — including concentration (80–700 mg/l Fe, 1–2% w/v oxalic acid), quality and intensity of illumination (e.g., daylight of illumination > 2500 lux), temperature (ambient), mode and intensity of agitation (slow stirring), and pH (<2) — the primary reaction (reduction of iron(III) to iron(II) with evolution of carbon dioxide from oxalate) largely occurred within 1–2 h. Following an induction period of several h during which the solution became supersaturated with respect to iron(II) and oxalate, well-formed yellow 10–40 Am crystals of FeC 2O 4 · 2H 2O (matching those reported in the literature) were precipitated over about 24 h. An excess of oxalic acid was necessary to maximise the rate of photochemical reaction and minimise re-oxidation (which caused an increase in pH and led to the precipitation of hydrated iron(III) oxide). For both thermodynamic and kinetic reasons, the extent of reaction was normally restricted to about 80% of the theoretical maximum. Photodecomposition was shown to be a potential continuous hydrometallurgical process meriting more detailed evaluation. Because of its relatively high purity and good handling characteristics, the precipitated iron(II) oxalate dihydrate represented a useful potential feedstock for added-value products, e.g., speciality iron oxides.

Quantitation of alkyltrimethylammonium bromides in Bayer process liquors by gas chromatography and gas chromatography-mass spectrometry

A sensitive and specific capillary gas chromatographic (GC) assay has been developed for the quantitation of the series of quaternary ammonium (QA) compounds, dodecyltrimethylammonium bromide (C12QA), tetradecyltrimethylammonium bromide (C14QA) and hexadecyltrimethylammonium bromide (C16QA) in high ionic strength, highly alkaline solutions. The procedure employed a single dichloromethane extraction of the iodide ion-paris of the QA compounds from pH-adjusted Bayer liquor, followed by injection (in methanol) onto the gas chromatography-mass spectrometry (GC-MS) system. Detection was based upon thermal dequarternisation of the QA-iodide complex in the injection port, with the corresponding tertiary amine (TA) analogue resolved by the GC system. Optimal extraction and GC conditions, as well as limits of detection and preliminary recoveries of these compounds, are reported. GC-MS, combined with injection of the pure TA analogues, was used to confirm the identities of the compounds eluted from the column.

Reactions of lime with aluminate-containing solutions

In the Bayer process for refining alumina, lime (either quicklime or slaked lime) is added to the process liquor to precipitate calcium carbonate and restore alkalinity to the solution. Lime also precipitates calcium aluminate in an unwanted side reaction which consumes both lime and aluminate. The work described in this paper was undertaken to elucidate the mechanism of this precipitation reaction about which little is known. The kinetics of the reaction between quicklime powder and aluminate in solution were studied as a function of stirring, reaction temperature, lime charge and sodium hydroxide concentration. It was concluded that the reaction was diffusion controlled, at least in the early stages. The second part of this study was directed towards assessing the effect of the calcium aluminate deposit on the lime slaking reaction. The kinetics of this reaction were investigated as a function of aluminate concentration, stirring, temperature and lime charge. The kinetic measurements were complemented by X-ray diffraction and scanning electron microscopy. It was found that the calcium aluminate deposit progressively shuts down the lime slaking reaction. If the aluminate concentration in solution is high enough, the lime particles are encapsulated by calcium aluminate and dissolution ceases.

Solvent extraction of gallium from an Indian Bayer process liquor using Kelex-100

Solvent extraction of gallium from a concentrated Indian Bayer process liquor was studied using 7-alkyl-substituted-8-hydroxyquinoline (Kelex-100) as an extractant and iso-decanol and kerosene as a modifier and a diluent, respectively. The composition of the Bayer process liquor was found to be ~450 gpl of Na 2 O, ~80 gpl of Al 2 O, and 190±20 ppm of gallium. The recovery percentage and the kinetics of extraction are improved by increasing the concentration of Kelex-100 in the organic phase from 6 to 14 vol%. However, the initial rate of extraction was slowed down at 16 and 18 vol% of Kelex-100. The initial rate of extraction was found to be improved by reducing the iso-decanol volume from 12 to 6% at 12 vol% of Kelex-100. The sodium and aluminium up take of the organic phase was found to be decreased with a decrease in the volume percent of iso-decanol. Minor additions of petroleum sulfonate improves the kinetics of gallium extraction significantly. The scrubbing of the loaded organic phase was found to be best at 6.0M HCl with a 1.0:1.5 organic to aqueous ratio, whereas, stripping was found to be best at 1.5M HCl with a 1.0:1.0 organic to aqueous ratio.

Determination of inorganic anions in Kraft pulping liquors by capillary electrophoresis

AbstractVarious sulfur containing anions (sulfate, sulfite, and thiosulfate) in Kraft pulping process liquors are determined by capillary electrophoresis. In addition, other inorganic anions (hydroxide, chloride, oxalate, carbonate) are analyzed with the developed method. Through optimization of the separation conditions it is possible to simultaneously determine these anionic species in pulping liquors with direct and indirect UV detection at 185, 214, and 254 nm. To ensure short separation times a migration of the anionic analytes in the same direction as the electroosmotic flow (co‐electroosmotic CE) is established by reversal of the electroosmotic flow with 1,5‐dimethyl‐1,5‐diazaundecamethylene polymethobromide (hexadimethrine bromide; HDB; polybrene™) which is added to the electrolyte as EOF modifier. The impact of acetonitrile as organic modifier to improve the selectivity of the anionic analytes is also investigated. The developed method is then applied to analyze and quantify various anions in pulping liquors (white and black liquors). By simultaneously determining the hydroxide concentration it is possible to calculate effective alkalinity and sulfidity with the measured concentrations without the need of volumetric methods.

Evolution of ozone for the bleaching of paper pulps

Abstract Although ozone has been studied seriously as a substitute for chlorine in the bleaching of pulp for paper making since 1949, it has only been since 1992 that ozone has begun to reach its full‐scale commercial potential. In this evolution, ozone has been aided immeasurably by environmental pressures to diminish the discharge of halogenated organics in pulp mill wastewaters. Thanks to the incorporation of ozonation into bleach processes, not only is the creation of halogenated organics minimized (and even eliminated in some cases), but this allows some of the processing liquors to be recovered and volumes of bleach plant effluents to be reduced. As a consequence, this not only decreases the volume of wastewater being discharged to the receiving water bodies, but also increases the potential for the Totally Effluent‐Free (TEF) bleached pulp mill to become a future reality. Ozone's evolution in this rapidly growing industry is traced, and some characteristics of the 14 full‐scale pulp mills currently using and five additional planning to use ozone for pulp bleaching in various parts of the world will be described.

A microwave digestion-based determination of low molecular weight organic acids in Bayer process liquor

A new technique for the determination of low molecular weight organic acids in Bayer process liquors is reported. The acids are partitioned from acidified liquor into butanol, followed by butylation using microwave heating. This method is both rapid (sample preparation time < 15 min) and capable of detecting acids larger than previously reported in the low molecular weight fraction (up to RMM 176). A standard solution containing 15 acids was used to calibrate the technique and 13 of these acids were detected and quantified in a Bayer liquor sample.

Determination of oxalate in alumina process liquors by ion chromatography with post column chemiluminescence detection

The analysis of oxalate in Bayer liquor had been successfully demonstrated using a combination of ion-exchange chromatography and post-column detection based on a chemiluminescence reaction with tris(2-2′bipyridyl)ruthenium(III). Common interferences, including other dicarboxylic acids and inorganic anions, have been shown to elicit no significant response. The chemiluminescence response is linear and a detection limit of 10–7 mol l–1 possible. The potential use of this method for other complex samples is presented. Chromatographic conditions provide a rapid analysis with sample analysis possible every 5–8 min.

Determination of carbohydrates in wood, pulp and process liquor samples by high-performance anion-exchange chromatography with pulsed amperometric detection

A rapid and sensitive method has been developed for the determination of monosaccharides present in the sulphuric acid hydrolyzates of wood, pulp, magnesium-based spent sulphite liquor, kraft weak black liquor and newsprint papermachine white water. Hydrolyzates were purified using an off-line, solid-phase extraction technique, employing cross-linked N-polyvinylpyrrolidone and strong anion- exchange resin. High-performance anion-exchange chromatography with pulsed amperometric detection was used to separate and quantify wood monosaccharides present in the purified hydrolyzates. Monosaccharide results obtained by ion and gas chromatographic methods were in good agreement for all samples examined. The effect of acid concentration on monosaccharide yields from the hydrolysis of process liquors was also investigated.