High Sulfuric Acid Concentrations Research Articles

Formation of Chromophores from cis-Pinonaldehyde Aged in Highly Acidic Conditions.

Sulfuric acid in the atmosphere can participate in acid-catalyzed and acid-driven reactions, including those within secondary organic aerosols (SOA). Previous studies have observed enhanced absorption at visible wavelengths and significant changes in the chemical composition when SOA was exposed to sulfuric acid. However, the specific chromophores responsible for these changes could not be identified. The goals of this study are to identify the chromophores and determine the mechanism of browning in highly acidified α-pinene SOA by following the behavior of specific common α-pinene oxidation products, namely, cis-pinonic acid and cis-pinonaldehyde, when they are exposed to highly acidic conditions. The products of these reactions were analyzed with ultra-performance liquid chromatography coupled with photodiode array spectrophotometry and high-resolution mass spectrometry, UV-vis spectrophotometry, and nuclear magnetic resonance spectroscopy. cis-Pinonic acid (2) was found to form homoterpenyl methyl ketone (4), which does not absorb visible radiation, while cis-pinonaldehyde (3) formed weakly absorbing 1-(4-(propan-2-ylidene)cyclopent-1-en-1-yl)ethan-1-one (5) and 1-(4-isopropylcyclopenta-1,3-dien-1-yl)ethan-1-one (6) via an acid-catalyzed aldol condensation. This chemistry could be relevant for environments characterized by high sulfuric acid concentrations, for example, during the transport of organic compounds from the lower to the upper atmosphere by fast updrafts.

Optimized Ilmenite Leachate by Wet Mechanical Activation for the Synthesis of TiO<sub>2</sub> Nanoparticles through Sulfate Route

The extraction of ilmenite minerals using the sulfate route is one of the commercial methods for producing titanium dioxide (TiO2) materials. The sulfate process requires a high concentration of sulfuric acid to achieve high extraction yield of titanium. However, this process also results in the generation of high amounts of sulfuric acid waste. Modifying ilmenite minerals is thought to be one of approaches in reducing the consumption of highly concentrated sulfuric acid. In the current study, we investigated the effect of the ilmenite-to-water mass ratio (ITWR) on the wet-ball milling process to enhance the dissolution of titanium from the ilmenite mineral. The results revealed that increasing the water amount from 10 to 70% wt has decreased the particle size from 167.60 to 0.55 μm and increased the titanium yield from 479.36 to 1228.89 ppm. On the basis of investigation, it was shown there is a significant relationship between the ilmenite-to-water mass ratio and titanium dissolution, highlighting the importance of an optimal ratio for achieving maximum dissolving yield. The obtained TiO2 nanoparticles provide the average crystallite size of 4.16 nm, with rutile and anatase phase, and spherical morphology.

Comparative Study on the Corrosion Behavior of Materials in Heat Recovery Steam Generators for Combined Cycle Power Plant, Based on Sulfuric Acid Concentrations: Carbon Steels vs. Duplex Stainless Steel (UNS S32205)

This study examined the effects of sulfuric acid concentrations on the corrosion behaviors of three types of commercial steels, conventional carbon steel (SA192), sulfuric acid dew resistant steel (S-TEN), and duplex stainless steel (S32205), considered to be potential materials for the heat recovery steam generator (HRSG) in combined cycle power plants. Based on the results of electrochemical polarization, immersion and wet-dry cycle tests, when exposed to a high sulfuric acid concentration (50%), SA192 and S-TEN exhibited higher corrosion resistance than S32205, which was due to the formation of a stable FeSO4 scale on the carbon steel materials. With prolonged exposure, S-TEN with slightly higher concentrations of Cu and Sb showed lower weight loss than SA192. Conversely, when subjected to low sulfuric acid concentrations (5 and 10%), S32205 exhibited passivation behavior, and showed significantly superior corrosion resistance (i.e., much smaller weight loss) than the other two steel samples. The examination of localized corrosion damages through cross-section observation using a scanning electron microscope revealed also that S32205 suffered less damages from the wet-dry cycling. The long-term superior corrosion resistance of duplex stainless steel in low sulfuric acid concentrations, compared to carbon steel and sulfuric acid due resistant steel, make it a promising candidate material for the HRSG in combined cycle power plants.

Evaluation of steam explosion pretreatment on the cellulose nanocrystals (CNCs) yield from poplar wood

The high sulfuric acid concentration used in the hydrolysis of cellulose to isolate cellulose nanocrystals (CNCs) leads to low yields due to the dissolution of both amorphous and semi-crystalline cellulose. The present study explored the use of steam explosion pretreatment before acid hydrolysis to enhance the crystallization of semi-crystalline/ non-crystalline cellulose and generating new CNC precursors with poplar wood as feedstock. The crystallinity of steam exploded poplar wood increased 1.3-fold compared to untreated poplar wood. Consequently, the overall yield of CNCs of steam exploded poplar wood increased 2.5-fold compared to untreated poplar wood. Moreover, the steam explosion pretreatment did not affect the quality of the CNCs with regard to the crystal size, crystallinity, and colloidal stability. Whereas the thermal stability of the CNCs increased due to the steam explosion pretreatment. This study demonstrates a simple and scalable pretreatment step that can significantly improve the CNCs yield from the acid hydrolysis step thereby improving the overall economics and commercial viability.

Direct generation of Zn metal using laser-induced ZnS to eradicate carbon emissions from electrolysis Zn production

In response to the goal of net-zero emissions proposed by Intergovernmental Panel on Climate Change, Chinese government has pledged that carbon emissions will peak by 2030, and achieve carbon neutrality by 2060. However, the high carbon energy structure of traditional industries has aggravated environmental problems, such as greenhouse effect and air pollution. The goal of carbon neutrality will be difficult to achieve without the development of disruptive theories and technologies. The electrolytic zinc industry requires high-temperature roasting at ∼1000 °C, generating large amounts of greenhouse gases and SO2. High concentrations of sulfuric acid (200 g/L) are subsequently used for electrolysis, and each ton of zinc produced generates 50 kg of anode slime with lead content of up to 16%, as well as 0.35 m3 of wastewater containing zinc and lead. To solve these problems, an optical metallurgy method is proposed in this study. The proposed method uses laser-induced photoreduction to decompose ZnS and reduce metal ions to metal. Results indicate that Zn0 and S8 can be detected on the surface of ZnS at a specific wavelength and laser fluence. The generation mechanism of Zn0 is such that laser induces an electronic transition that breaks ionic bond in ZnS, resulting in its decomposition and photoreduction to Zn0 under an inert argon gas atmosphere. This method does not reduce other metals in the mineral since it does not use high-temperature roasting, providing a new way of producing high-purity metal without greenhouse gas emissions and heavy metal pollution caused by traditional zinc electrolysis.

COMBINATION OF COPPER INTERMEDIATE SX STEEL AND GR5 (Ti6Al4V) TITANIUM BY DIFFUSION WELDING METHOD

GR5 (Ti6Al4V) is a material commonly used in aerospace and space, biomedical and automobile sectors, consisting of pure titanium at a minimum of 99% purity. Besides being lightweight, GR5 is separate from similar materials with its ability to resist corrosion at high levels and show high strength. SX steel is high silicon-content austenitic stainless steel with the ability of good quality of welding and excellent corrosion resistance in high concentration sulfuric acid and nitric acid. SX is used in areas such as acid coolers, acid piping systems, acid distributors, acid towers and tanks, pumps, nozzles, internals, strainers and mesh pads. With improving technology, the need for steel-titanium materials that are resisted to acid and made with welded joint is increasing. In this study, the effect of GR and SX materials of welding temperature on the connection is examined with diffusion welding method using copper intermediary layer. The material pairs are combined with a pressure of 5 MPa and a fixed welding time of 60 minutes in an argon gas environment in a silicon bar oven at the temperature of 980, 1000 and 1020°C. The SEM-EDS-AFM analysis of the combined samples is performed, the metallographic structure of the intermediary layer in the diffusion-affected region is examined by the optical microscope, and the possible phases are tried to be determined by the XRD analysis. The micro stiffness values of the connection area are analyzed.

Optimization of the electrolytic production of Caro’s acid. Towards industrial production using diamond electrodes

The production of oxidants to apply in different disinfection processes is of outstanding importance. Among all, peroxosulfate species, and especially the Caro’s acid, are of a primary importance, because they can be stored and further electrochemically or UV-light activated for the target process, unlike other oxidants like ozone or chlorine dioxide. In this work, Caro’s acid has been produced using boron-doped diamond (BDD) electrodes and an innovative tailored electrochemical cell manufactured by 3D printing. Several operating conditions like temperature, current density, and electrolyte concentration have been studied. Regarding these variables, minor improvements in the production of Caro’s acid were achieved when the temperature was reduced, being more significant the improvement observed with the increase in the current density (concentration of 250 mM at 9 °C and 300 mAcm−2 were obtained feeding 1 M of H2SO4). Considering the electrolyte concentration, a high concentration of sulfuric acid allowed to produce larger concentrations of Caro’s acid (517 mM using 5 M of H2SO4), but within a matrix with more unreacted H2SO4. Furthermore, the process has also been conducted in divided cells (two compartments) and outstanding concentrations of around 400 mM were achieved. For operation in on-line applications, a continuous mode of production has been studied, resulting in a very predictable behavior, which is important for the future scalability of the process. Finally, a phenomenological model has been proposed and validated by fitting experimental results. This model also contributes to scale up the process and allows to fully understand and control the operational conditions and its influence on the reaction.

Selective removal of copper from heavy-metals-containing acidic solution by a mechanochemical reduction with zero-valent silicon

It is always a challenge to deal with industrial wastewater containing heavy metals. Selective removal and recovery of valuable metals such as copper particularly from acidic solutions are very important from both stances of resource supplying and environmental purification. Among all the divalent heavy metals, copper has the potential of being reduced to monovalent state. A new approach was proposed to ball mill zero-valent silicon (ZVS) in CuSO4 solution and the solutions containing multi-metal ions to serve the purpose. In this study, both quantitative and qualitative data were reported on the induced mechanochemical reduction reaction to convert Cu2+ into Cu2O by ball milling with ZVS. Experimental parameters such as milling time and Si to Cu ratio were found to play important role in stimulating the reaction, and as a result, 97.32% Cu2+ was removed from the solution under Si/Cu molar ratio of 100. Even at a high concentration of sulfuric acid up to 4.6 mol/L, the copper removal percentage maintained a high value of 82.57%. Furthermore, in the sulfate solutions containing several other heavy metals of Zn, Mn, Ni, Cd, Co, Fe etc., the reduction reaction by zero-valent silicon occurred only on Cu2+ with other heavy metal ions remaining in the solutions. The feasibility of this technology has been verified by treating a leaching solution of NiS mineral, from which copper has been removed selectively from nickel, iron etc. This research may serve another purpose for applying waste silicon from the solar energy devices after lifetime in the future.

Effect of acid concentration on organic structure and small molecule stripping of coal during acid treatment and electrolysis for hydrogen production

Coal-assisted water electrolysis for hydrogen production can effectively reduce electricity consumption and improve the economics of electrolytic hydrogen production technology. However, the influencing factors of this process, especially the mechanism of the electrolyte itself on the coal particles, are not clear. The influence of electrolyte on the electrooxidation process of coal particles is of great importance in practical applications. In this paper, detailed controlled experiments were designed to investigate the effect of electrolyte concentration on coal-assisted water electrolysis. And the laws of the acid leaching and electrooxidation processes on the macrostructure and organic structure of coal particles were investigated by various characterization methods. Information on the small molecules of organic matter stripped from coal molecules under different experimental conditions was also obtained by GC–MS. The results showed that the reactivity of coal particles decreased with increasing electrolyte concentration, and judging reactivity from current density alone would produce some errors. The rebound of current density in high concentration of sulfuric acid mainly came from more fragmentation of coal particles. The CO structure played a facilitating role in the oxidation of coal, while the CO and COOH structures would hinder the further oxidation of coal particles due to their stability. Small organic molecules were released from coal particles into the electrolyte during acid leaching and electrolysis, and the amount of small organic molecules detached was positively correlated with sulfuric acid concentration and oxidation charge, where oxidation detachment dominated.

The influence of the electrolytic bath on the hard anodizing of diecast Al–Si–Cu alloys

In the present work, the influence of the temperature and concentration of the electrolyte on the anodizing response of a high-pressure diecast AlSi11Cu2(Fe) alloy was studied. Sandblasted components, produced by high pressure diecasting, were anodized at −4.5 °C or +5 °C in an electrolyte with a free sulfuric acid concentration of 168 g/L or 217 g/L. Metallographic and image analysis techniques were carried out to study the changes in the oxide layer in terms of thickness and morphology. Scratch and wear tests were also performed to characterize the surface mechanical properties. The results show how the thickness of the anodic layer can be increased by decreasing the anodizing temperature of the electrolytic bath otherwise increasing the concentration of the sulfuric acid. However, the combination of a low anodizing temperature and a high concentration of free sulfuric acid has no beneficial effect on the formation of the anodic film. In this condition, the dissolution phenomena of the oxide layer inside the electrolyte are promoted and a thinner low-performance anodic layer is formed. Finally, the wear and scratch resistance are maximized after anodizing at −4.5 °C in an electrolyte with a concentration of sulfuric acid equal to 168 g/L.

Insufficient Condensable Organic Vapors Lead to Slow Growth of New Particles in an Urban Environment.

Atmospheric new particle formation significantly affects global climate and air quality after newly formed particles grow above ∼50 nm. In polluted urban atmospheres with 1-3 orders of magnitude higher new particle formation rates than those in clean atmospheres, particle growth rates are comparable or even lower for reasons that were previously unclear. Here, we address the slow growth in urban Beijing with advanced measurements of the size-resolved molecular composition of nanoparticles using the thermal desorption chemical ionization mass spectrometer and the gas precursors using the nitrate CI-APi-ToF. A particle growth model combining condensational growth and particle-phase acid-base chemistry was developed to explore the growth mechanisms. The composition of 8-40 nm particles during new particle formation events in urban Beijing is dominated by organics (∼80%) and sulfate (∼13%), and the remainder is from base compounds, nitrate, and chloride. With the increase in particle sizes, the fraction of sulfate decreases, while that of the slow-desorbed organics, organic acids, and nitrate increases. The simulated size-resolved composition and growth rates are consistent with the measured results in most cases, and they both indicate that the condensational growth of organic vapors and H2SO4 is the major growth pathway and the particle-phase acid-base reactions play a minor role. In comparison to the high concentrations of gaseous sulfuric acid and amines that cause high formation rates, the concentration of condensable organic vapors is comparably lower under the high NOx levels, while those of the relatively high-volatility nitrogen-containing oxidation products are higher. The insufficient condensable organic vapors lead to slow growth, which further causes low survival of the newly formed particles in urban environments. Thus, the low growth rates, to some extent, counteract the impact of the high formation rates on air quality and global climate in urban environments.

Experimental based CO2 transport specification ensuring material integrity

Material choice has a large impact on the total cost of the CO2 transport system for carbon capture and storage (CCS). Cost-considerations make carbon steel the preferred candidate for long pipelines. As carbon steel will corrode if aqueous phases are present, it is important to control the CO2 composition and operate the system such that formation of water containing phases is avoided.There are many suggested specifications and recommendations for the type and concentration of impurities to be allowed in the CO2 stream. The impurity limits were often set from a health, safety, and environmental point of view and are due to lack of knowledge not so much based on material integrity issues. This gap of knowledge makes it difficult to define a specification that will ensure safe operation and long-term integrity.The present paper summarises the results of a large research project that systematically tested CO2 with various combinations and concentrations of potentially reactive impurities (H2O, NO2, SO2, H2S, O2). It was clearly shown that many impurity combinations were basically inert, while other resulted in chemical reactions and some combinations even resulted in the formation of a separate aqueous phase that contained high concentrations of sulfuric and nitric acid as well as elemental sulphur. This aqueous phase was corrosive to carbon steel. Corrosion was also observed in certain situations even when a separate aqueous phase was not observed visually.It is important to avoid precipitation of solid products since it may cause problems at the injection point and in the reservoir. The present work demonstrated that the types and combination of impurities that are present are important for the maximum impurity concentration that can be allowed before chemical reactions and corrosion occur. For the investigated conditions, 100 bar and 25 °C, the concentration limit for each impurity should be below 20 ppmv if NO2, SO2, H2S, O2 are present together. The limits may be different at other temperatures and pressures.

Electrode optimization for efficient hydrogen production using an SO2-depolarized electrolysis cell

The hybrid sulfur (HyS) cycle offers an alternative route to hydrogen and sulfuric acid production using the SO2-depolarized electrolysis (SDE) cell. This work reports the most efficient SDE operation to date at high sulfuric acid concentrations (∼60 wt%) achieved through the optimization of operating conditions and cell components. We observed that open porosity in the porous transport media (PTM) plays a significant role in SDE performance as it enables efficient acid removal from the catalyst layer. The combination of membrane electrode assembly (MEA) components, such as Sulfonated Diels Alder Poly (phenylene) (SDAPP) membranes and electrodes prepared using SGL 29BC PTM, and operating conditions (103.4 kPagauge at 125 °C) yielded electrolysis potentials <700 mV at 500 mA/cm2 and acid concentrations >60 wt%.

Measurement report: Long-term measurements of aerosol precursor concentrations in the Finnish subarctic boreal forest

Abstract. Aerosol particles form in the atmosphere via the clustering of certain atmospheric vapors. After growing into larger particles by the condensation of low-volatility gases, they can affect the Earth's climate by scattering light and acting as cloud condensation nuclei (CCN). Observations of low-volatility aerosol precursor gases have been reported around the world, but longer-term measurement series and any Arctic data sets showing seasonal variation are close to nonexistent. Here, we present ∼7 months of aerosol precursor gas measurements performed with a nitrate-based chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometer. We deployed our measurements ∼150 km north of the Arctic Circle at the SMEAR I (Station for Measuring Ecosystem–Atmosphere Relations) continental Finnish subarctic field station, located in the Värriö strict nature reserve. We report concentration measurements of the most common compounds related to new particle formation (NPF): sulfuric acid (SA), methane sulfonic acid (MSA), iodic acid (IA) and the total concentration of highly oxygenated organic molecules (HOMs). At this remote measurement site, SA originates from both anthropogenic and biological sources and has a clear diurnal cycle but no significant seasonal variation. MSA shows a more distinct seasonal cycle, with concentrations peaking in the summer. Of the measured compounds, IA concentrations are the most stable throughout the measurement period, except in April during which time the concentration of IA is significantly higher than during the rest of the year. Otherwise, IA has almost identical daily maximum concentrations in spring, summer and autumn, and on NPF event or non-event days. HOMs are abundant during the summer months and low in the autumn months. Due to their low autumn concentrations and high correlation with ambient air temperature, we suggest that most HOMs are products of biogenic emissions, most probably monoterpene oxidation products. NPF events at SMEAR I happen under relatively low-temperature (1–8 ∘C) conditions, with a fast temperature rise in the early morning hours as well as lower and decreasing relative humidity (RH, 55 % vs. 80 %) during NPF days compared with non-event days. NPF days have clearly higher global irradiance values (∼450 m−2 vs. ∼200 m−2) and about 10 ppbv higher ozone concentrations than non-event days. During NPF days, we have, on average, higher SA concentrations, peaking at noon; higher MSA concentrations in the afternoon; and slightly higher IA concentration than during non-event days. In summary, these are the first long-term measurements of aerosol-forming vapors from SMEAR I in the subarctic region, and the results of this work will help develop an understanding of atmospheric chemical processes and aerosol formation in the rapidly changing Arctic.

The Ionic State of Molybdenum in Sulfuric Uterine Solutions of Rhenium Sorption and its Extraction

results of studies of the forms of finding and methods of extracting molybdenum from acidic solutions with a high concentration of sulfuric acid are presented. Ion-exchange resins of various modifications were tested to determine the most effective for molybdenum during its sorption from a sulfuric acid solution.

Ionic State of Molybdenum in Sulfuric Uterine Solutions of Rhenium Sorption and its Extraction

The results of studies of the forms of finding and methods of extracting molybdenum from acidic solutions with a high concentration of sulfuric acid are presented. Ion-exchange resins of various modifications were tested to determine the most effective for molybdenum during its sorption from a sulfuric acid solution.

Biogas Production from Sugarcane Vinasse: A Review

Biogas is a renewable energy sources that could replace the role of fossil fuel. Biogas could be produced from biomass or agro-industrial wastewater. Sugarcane vinasse has potential of biogas production due to its high BOD concentration (10–65 g BOD/l). However, the biogas production from sugarcane vinasse has several drawbacks that hinders the maximum biogas yield, such as: acidic pH (pH 3.5 – 5.0), high temperature (80–90°C) and high concentration of sulfuric acid (&gt; 150 mg/L). Theoretically, the methane potential per gram COD is 0.35 L/gr COD, containing of 60% methane. However, up to date, the maximum biogas production from vinasse was less then its theoretical value. To get the full potential of biogas production from vinasse wastewater as well as to reduce the capital cost for full scale application, combination of suitable pre-treatment, selected microorganisms and bioreactor design-configuration are the most important parameters to be considered. This paper aims to explore the potential of sugarcane vinasse to produce biogas, by elaborating the aforementioned key parameters. In this review the basic characteristic and the potency of sugarcane vinasse wastewater will be elaborated. Furthermore, the effect of key parameters such as pH, temperature, and organic load to biogas production will also be discussed. The biogas technology will also be explored. Lastly, conclusion will be determined

Detection of Galactose and Glycerophospholipids by Galactose Biosensors and Advancement Their Proficiency Using Berkelium Colloidal Nanoparticles and Poly(3,4-Ethylenedioxythiophene)-Poly(Styrenesulfonate)-Based Biosensors

In the current paper, galactose-oxidase enzyme is used as stabilization medium due to its more proficiency, ability for more accurate controlling the enzyme reaction, protecting against wasting of enzyme as well as simple and easy use and exchange of enzyme medium after performing some levels of surface modification and developing multi-walled carbon nanotubes (MWCNTs) on Berkelium plate. For better connecting and stabilizing the enzyme on the medium, the prepared medium is washed by high concentration sulfuric acid and nitric acid and a large volume of deionized water and for protecting enzyme from devastating effect of Berkelium and prohibiting them to become inactive, surface is covered with cystamine before stabilization. Regarding the large size of galactose-oxidase enzyme compared to surface of medium, a connective material with amid at one end and pyrine at the other end is used as transfer agent and for stabilizing this connection, the prepared medium is placed into dimethylformamide (DMF) solution for a couple of hours. Activity of stabilized enzyme at 460 (nm) wavelength recorded by spectroscope was depicted against time to evaluate its stability in various times. The prepared medium, which have a large amount of galactose-oxidase enzyme, can be used as electrode in sensors. Furthermore, galactose-oxidase electrochemical sensor is one of the best methods for detecting low amount of galactose and applying Berkelium colloidal nanoparticles as a supplementary material in the structure of biosensor can be effective for advancement its proficiency and optimum proficiency. On the other hand, in the current study, electrode biosensor entitled as modified carbon paste electrode with Berkelium colloidal nanoparticles (Bknano/CPE) is produced by carbon graphite powder, paraffin oil and Berkelium colloidal nanoparticles (24 nm) and it is compared with carbon paste electrode (CP). In semi-permeable membranes, a combination of 1 (ml) of 0.1 (M) phosphate buffer with specified pH and 10 (mg) of galactose-oxidase enzyme is placed around each electrode. In the same potential of 0.7 (V), biosensors are tested with galactose in concentration range of (0-1) (mM) and various amounts of pH (4,6,8) which lead to producing the maximum current and tracing galactose in pH=6 and concentration of 1 (M) as the optimum condition. Currentmetry induced from both biosensors are compared and it is confirmed that using Berkelium colloidal nanoparticles in the structure of (Bknano/CPE) electrode leads to increasing the conductivity and currentmerty of biosensor. In addition, qualitative and quantitative measurement of food components is of great importance due to high cost of traditional methods, in addition to tendency for more accurate and sensitive detecting of these components. galactose and glycerophospholipids are such compounds that they frequently measure. Various methods are used to detect these food elements. However, the necessity for accurate measurement of these two compounds with high sensitivity, especially for food health issue, leads to developing biological methods, especially biosensors. Among them, biosensors based on conductive polymer nanostructures, especially Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), have been recently interested due to their unique characteristics. The current paper aims to introduce and investigate the previously performed studies about Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)-based biosensors for detecting galactose and glycerophospholipids.

Leaching kinetics of low nickel matte in an aqueous solution of sulfuric acid saturated with FeSO4 and NiSO4

• The oversaturated sulfate solution leaching of low nickel matte was proposed. • Leaching kinetics of low nickel matte in the saturated solution was investigated. • Compared with H 2 SO 4 leaching, the reaction rate in saturated solution was slower. • The nickel dissolution was controlled by diffusion through the inert porous layer. • The leaching kinetic equation is: 1 - 2 x / 3 - 1 - x 2 / 3 = 3.0 × 10 - 2 C 0 3.02 · r 0 - 2 · exp ( - 48741 / R T ) · t . In the previous study of our group, the low nickel matte was leached directly using H 2 SO 4 under atmospheric pressure. As long as the acidity of the solution was high enough, the high-efficiency leaching of iron, cobalt and nickel can be realized. Moreover, the cuprous sulfide and precious metals cannot be decomposed by H 2 SO 4 and were enriched in the leach residue. Due to the high concentration acid used in the leaching process of low nickel matte, the residual acid in leaching solution may need to be neutralized firstly before the subsequent metal separation. However, a lot of alkali will be consumed, resulting in the formation of harmful inorganic salts. In the experiments, we found that sulfate in the leaching solution could reach saturated and continuously crystallized out under the condition of high concentration of sulfuric acid. Based on the above considerations, the crystallization method may be a choice. Upon combination of the leaching and crystallization process, a new way to extract valuable metals and effectively recycle the sulfuric acid was proposed. However, the dissolution of low nickel matte will be also affected when the solution is saturated. Therefore, it is necessary to explore the leaching behavior of low nickel matte in the presence of solutions saturated with sulfate. In this study, the leaching kinetics of low nickel matte in H 2 SO 4 solutions saturated with FeSO 4 and NiSO 4 was investigated. Kinetic data of the dissolution of nickel for various parameters showed best fit to the kinetic model governed by diffusion in the inert porous media. The results shown that the reaction order of H 2 SO 4 was 3.02 and the activation energy of the system was found to be approximately 48.7 kJ·mol −1 . Compared with sulfuric acid leaching, the reaction order of this study increased greatly, which indicated that the influence of acid concentration on leaching process increased. In addition, the decrease of activation energy showed that the oversaturated sulfate solution leaching process was consistent with the internal diffusion control, which may be because the existence of crystal had an effect on the diffusion of H + ions in pores.

Removal of Fe(III) from sulfuric acid leaching solution of phosphate ores with bisphosphonic acids

Iron(III) in phosphate ore leach liquor harms the quality of phosphoric acid and phosphogypsum crystallization. In this paper, the selective separation of iron(III) was studied with two novel extractants, N, N-n-octylamine di(methylene phenylphosphonic acid) (OADMPPA) and N, N-n-hexadetamine di(methylene phenylphosphonic acid) (HADMPPA), from a mixed media of sulfuric acid and phosphoric acid. The effects of temperature, time, diluents, and the concentrations of sulfuric acid and extractant on the separation of iron were investigated. The mechanism of extraction was established by UV–Vis spectroscopy, FT-IR spectroscopy, slope analysis, and the equimolar series method. The results showed that the two new reagents have good extraction ability toward iron(III) even at higher sulfuric acid concentration. Both OADMPPA and HADMPPA can remove more than 99% of iron(III) from the sulfuric acid leach liquor of phosphate ore. The stripping of iron(III) from the organic phase after extraction with acidic phosphine (phosphorus) extractants was difficult. Oxalic acid was found to be a good stripping agent. The single stage stripping efficiency reached 62.8%, and the two-stage stripping efficiency could reach over 99%. The separation and recovery of iron(III) in phosphate ore leach liquor could be realized by our method without changing the traditional phosphoric acid production process, which is beneficial to the purification of phosphoric acid and the recovery of iron.