Study on sulfur migration in activated carbon adsorption-desorption cycle: Effect of alkali/alkaline earth metals

Adsorption of sulfur on Lanxess Lewatit® AF 5 resin during the acidic albion leaching process for chalcopyrite

Elemental sulfur is one of the major byproducts of the acidic Albion leaching process for chalcopyrite. It is a challenging component in the leach solution as it impedes gold recovery from the residue. Lanxess Lewatit® AF 5 (AF 5) is a microporous carbon-based resin, which is being investigated for the removal of elemental sulfur during this leaching process. In the current research, a series of leaching experiments were performed as a function of temperature, agitation speed and concentrate to AF 5 ratio. Using these results, the adsorption isotherms, the kinetics and the thermodynamics of sulfur removal were studied. One hundred percent of the elemental sulfur could be adsorbed by the AF 5 resin from the acidic Albion leaching process for chalcopyrite. Adsorption isotherms at various temperatures were determined using the Langmuir and Freundlich models. The maximum sorption capacity of AF 5 at 95 °C was 488 mg/g. The kinetic data were fitted to pseudo-first order (PFO) and pseudo-second order (PSO) models and it was shown that the PFO model was best suited to describe the results. The rapid kinetics of sulfur adsorption were attributed to the open pore structure of the AF 5. The Gibbs free energy, enthalpy and entropy of sulfur adsorption by AF 5 were determined as follows: ΔG_ads ^o = -1.9 kJ/mol, ΔH_ads ^o = -9.1 kJ/mol, and ΔS_ads ^o = -0.1 kJ/(mol K). The negative free energy and enthalpy changes demonstrated that the adsorption of elemental sulfur was both spontaneous and exothermic over the temperature range studied.

The recovery of strontium ions from seawater reverse osmosis brine using novel composite materials of ferrocyanides modified roasted date pits

In this study, three types of adsorbents were used to remove and recover strontium ions (Sr2+) from aqueous and brine solution of seawater reverse osmosis (SWRO), namely roasted date pits (RDP) and RDP modified using copper and nickel salts of potassium hexacyanoferrates to obtain RDP-FC-Cu, and RDP-FC-Ni, respectively. Additionally, the influence of various parameters, including pH, temperature, initial concentration, and co-existing ions was also evaluated. The results revealed that pH 10 was the optimum pH in which the maximum Sr2+ ions were adsorbed. Additionally, all adsorbents had a high adsorption capacity (99.9 mg/g) for removing Sr2+ ions at the highest concentration (100 mg/L) and a temperature of 45 °C was found to be the optimum temperature. A scanning electron microscopy for the adsorbents before and after the adsorption of strontium showed the remarkable pore filling onto the active sites of all adsorbents. The thermodynamics parameter demonstrated that the adsorption occurred in an endothermic environment, and that, the reaction was spontaneous, and favorable at all the temperatures investigated. According to isotherm studies, the Langmuir model was the best-fit isotherm model; indicating that strontium adsorption involved the formation of monolayers and multilayers at higher temperatures (45 °C). Furthermore, high desorption percentages (above 90%) were achieved for all the adsorbents when an HCl concentration of 0.5 M was used. This showed the high reusability of the adsorbents. Lastly, the adsorption of strontium from the SWRO brine containing a number of metal ions was extremely sufficient as all the adsorbents were efficient to adsorb a high amount of Sr2+ despite the presence of other competing ions.

Insight into the Transformation Behaviors of Dioxins from Sintering Flue Gas in the Cyclic Thermal Regeneration by the V2O5/AC Catalyst-sorbent

Dioxins in the sintering flue gas are usually removed through integrated elimination technologies by carbonaceous catalysts. However, the regeneration of the used catalyst is poorly investigated, leading to the risk of leakage of dioxins. Herein, the influences of cyclic regenerations on the dioxin removal performance of a catalyst (V₂O₅/AC) were investigated systematically with dibenzofuran (DBF) as a model pollutant. It was demonstrated that the adsorption capacity and oxidation activity of catalysts significantly declined after several regeneration cycles due to the decreasing external specific surface area and V⁵⁺, respectively. Compared with 79.12% DBF directly emitted from a regenerator during N₂ regeneration, the emission of DBF was only 29.93% with the modification of the regeneration process through O₂ addition and temperature adjustment. The possible regenerated products were also analyzed to disclose the transformation behaviors of DBF. The regeneration mechanisms of DBF followed the transformation pathway of dibenzofuranol, benzofuran, anhydride species, and ultimately to CO₂ and H₂O. Moreover, the accumulated heavy aromatics on the surface could be decomposed by introducing O₂. This research provides a comprehensive understanding of dioxin transformation behavior and a theoretical basis for efficient control of dioxin removal in the whole integrated removal technologies.

Carbon consumption and regeneration of oxygen-containing functional groups on activated carbon for flue gas purification

High carbon consumption is an important factor restricting the wide application of activated carbon technology for flue gas purification. A fixed-bed reactor combined with a Fourier transform infrared (FTIR) spectrometer was used to explore the source of carbon consumption at various SO₂ concentrations and cyclic adsorption-regeneration times. The results demonstrate that carbon consumption originates from two sources and is mainly determined by the reaction of H₂SO₄ and C at high SO₂ concentrations and by the thermal decomposition of oxygen-containing functional groups at low SO₂ concentrations. An interesting observed phenomenon is that carbon consumption does not increase as the SO₂ concentration increases. The conversion mechanism reveals that carboxylic and anhydride groups are converted to phenol and quinone groups, which do not easily decompose with increasing SO₂ concentration. In the process of cyclic adsorption-regeneration, it is discovered that the carbon consumption in the first cycle is several times higher than that in the following cycles due to the decomposition of functional groups from the activated carbon itself. The regeneration mechanism of functional groups has been elucidated. The carboxylic acid and the phenolic hydroxyl on the surface of activated carbon are consumed in the regeneration process and formed again from the conversion of carbonyl groups in the next adsorption process under the roles of O₂ and H₂O. It is proposed that the functional groups are regenerated in the adsorption process rather than in the regeneration process.

Novel composite materials of modified roasted date pits using ferrocyanides for the recovery of lithium ions from seawater reverse osmosis brine

In this paper, novel composite materials from modified roasted date pits using ferrocyanides were developed and investigated for the recovery of lithium ions (Li+) from seawater reverse osmosis (RO) brine. Two composite materials were prepared from roasted date pits (RDP) as supporting material, namely potassium copper hexacyanoferrate-date pits composite (RDP-FC-Cu), and potassium nickel hexacyanoferrate-date pits composite (RDP-FC-Ni). The physiochemical characterization of the RO brine revealed that it contained a variety of metals and salts such as strontium, zinc, lithium, and sodium chlorides. RDP-FC-Cu and RDP-FC-Ni exhibited enhanced chemical and physical characteristics than RDP. The optimum pH, which attained the highest adsorption removal (%) for all adsorbents, was at pH 6. In addition, the highest adsorption capacities for the adsorbents were observed at the initial lithium concentration of 100 mg/L. The BET surface area analysis confirmed the increase in the total surface area of the prepared composites from 2.518 m2/g for RDP to 4.758 m2/g for RDP-FC-Cu and 5.262 m2/g for RDP-FC-Ni. A strong sharp infrared peak appeared for the RDP-FC-Cu and RDP-FC-Ni at 2078 cm-1. This peak corresponds to the C≡N bond, which indicates the presence of potassium hexacyanoferrate, K4[Fe(CN)6]. The adsorption removal of lithium at a variety of pH ranges was the highest for RDP-FC-Cu followed by RDP-FC-Ni and RDP. The continuous increase in the adsorption capacity for lithium with increasing initial lithium concentrations was also observed. This could be mainly attributed to enhance and increased lithium mass transfer onto the available adsorption active sites on the adsorbents' surface. The differences in the adsorption in terms of percent adsorption removal were clear and significant between the three adsorbents (P value < 0.05). All adsorbents in the study showed a high lithium desorption percentage as high as 99%. Both composites achieved full recoveries of lithium from the RO brine sample despite the presence of various other competing ions.

Intensification of NO x Conversion over Activated Coke by Ozone Oxidation for Sintering Flue Gas at Low Temperatures

Denitration (De-NO x ) over activated cokes (ACs) for sintering flue gas needs intensification. Gaseous reactions in a gas mixture containing NO, NO2, and NH3, with the effect of O2 concentration and moisture, were taken into consideration in the study of NO x conversion over ACs. Experimental studies on NO x conversion with and without NH3 over ACs were conducted using a fixed-bed reactor at 100 °C. The results demonstrated that moisture significantly affected NO x removal over ACs, especially the NO2 conversion. Under dry conditions, a disproportionation reaction of NO2 over ACs dominated NO x conversion with no NH3, whereas apparent fast selective catalytic reduction (SCR) over the ACs was observed in the presence of NH3. Regardless of the presence of absence of NH3 in wet mixtures, NO2 adsorption on ACs via the disproportionation route dominated the NO x conversion. Increasing the NO2/NO ratio in the simulated flue gas enhanced the NO x conversion rate over ACs. -C(ONO2) deposition on ACs generated by the disproportionation route inhibited NO x conversion with time. O3 oxidation was found to be efficient in increasing the NO2/NO ratio and intensifying the NO x conversion compared with commercially direct NH3-SCR over ACs. Increasing the temperature and decreasing the gas hourly space velocity can promote NO x conversion over ACs after O3 oxidation. NO oxidized with O3 coupled with NH3 spray and continuous regeneration of ACs is a potential method for removing NO x from sintering flue gas.