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Silica-based aerogel composite was prepared adopting sol–gel technique combined with atmospheric drying method utilizing waste environmentally hazardous iron tailings. High-temperature alkali fusion was applied to extract the Si, Al and Fe in the tailings so as to maximize recovery of valuable elements. The SiO2-Al2O3 (SA) and SiO2-Al2O3-Fe2O3 (SAF) aerogel composites were subjected to assess its adsorption capacity for macromolecules, utilizing methylene blue (MB) as the adsorbate. The specific surface areas of the SA and SAF aerogel were estimated to be 922.03 m2/g and 683.84 m2/g. The equilibrium adsorption capacity for MB was estimated to be 318.47 mg/g and 334.44 mg/g, respectively. Although the specific surface area of SAF was lower than SA, it offered higher MB adsorption capacity which could be attributed to the presence of iron oxide. The results promised utilization of iron tailing generated aerogel composite as a potential adsorbent for separation of high molecular weight compounds.

Microwave technology is being increasingly explored in metallurgical processes. The dielectric properties characterize the action mechanism between electromagnetic energy and minerals. Here, a cavity perturbation method was used to survey the dielectric properties of zinc sulfide concentrate with sodium peroxide additive from 20°C to 600°C at 2.45 GHz. The effects of sodium peroxide additives and temperature on the dielectric properties were investigated. Theoretical analyses showed that the zinc sulfide concentration could be heated quickly when the concentration of sodium peroxide was greater than or equal to 6 wt.%. The heating mechanism is mainly Joule heat loss caused by ionic conduction of sodium peroxide. The heating rate comes from energy conversion and heat conduction at temperatures higher than 400°C. Microwave heating experiments and phase formation verified the correctness of the theoretical analyses. The results provide a better understanding of the microwave roasting mechanism of zinc sulfide concentrate, but also support the use of sodium peroxide as a means to promote thermochemical treatments by microwave irradiation.

Manganese ore is an important mineral having a strategic role in the development of the national economy and society. In this study, the dielectric properties, heating curve, crystal structure, and reduction ratio of a low-grade pyrolusite were investigated. The dielectric constant, dielectric loss factor, and loss tangent coefficient of low-grade pyrolusite at room temperature were evaluated using the resonant cavity perturbation method, yielding values of 5.854, 0.146, and 0.0249, respectively. Owing to the excellent microwave absorption properties of low-grade pyrolusite with 10% coal (22 g), it could be heated to a temperature of 800°C within 200 s. X-ray diffraction results confirmed that MnO2 was partially transformed into MnO at 450°C, while, at 650°C, no diffraction peak of MnO2 was observed. At a reduction temperature of 550°C, a reduction ratio of MnO2 to MnO of 96.65% could be achieved within a holding time of 50 min. This study demonstrates that the microwave carbothermal reduction of a low-grade pyrolusite is efficient, and thus could promote the clean production and sustainable development of the manganese industry.

The potential of utilizing shiitake mushroom as feed stock for the preparation of activated carbon by chemical activation method with $$\text {K}_{2}\text {CO}_{3}$$ was explored. The prepared materials were characterized by thermogravimetric analysis, $$\text {N}_{2}$$ adsorption–desorption analysis, scanning electron microscope, Fourier transform infrared spectrometer, X-ray diffraction and Raman spectra. The activation mechanisms were proposed with the aid of thermogravimetric analysis. X-ray diffraction and Raman analysis indicated that the activated carbon was amorphous macroscopically. The influences of activation temperature, mass ratio of $$\text {K}_{2}\text {CO}_{3}$$ /shiitake mushroom, activation duration, heating rate and material mixed mode on the yield, porosity and surface morphology of the activated carbon were investigated in detail. The synthesized activated carbons was predominantly microporous having a specific surface area of 2330 m $$^{2}$$ /g, and the optimal process conditions were activation temperature of 800 $$^{\circ }$$ C, mass ratio of $$\text {K}_{2}\text {CO}_{3}$$ /shiitake mushroom of 1.5, activation duration of 180 min, heating rate of 5 $$^{\circ }$$ C/min and mixed mode of impregnation. Addition to high surface area, it also exhibited a high iodine number adsorption capacity of 1432 mg/g and methylene blue adsorption capacity of 872 mg/g, which are far higher than the adsorption capacities reported in the open literature. These results demonstrate that the synthesized activated carbon could be utilized for variety of industrial applications.

A novel adsorbent was synthesized by functionalizing nanosilica with phosphinic acid groups for the removal of mercury ions from aqueous solutions. The synthesized absorbent was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and thermogravimetric analysis (TGA). Meanwhile, the effects of initial pH, contact time and initial mercury ions concentration on the removal of mercury ions from aqueous solutions were investigated by batch adsorption experiments. The results showed that the removal rate reached 99.11% and the maximum adsorption capacity was up to 274.32 mg/g at pH 2 and the equilibrium time of adsorption was about 1 h. The absorbent presented good selectivity for mercury ions among Zn(II), Ni(II), Mn(II) and Ge(IIII). Moreover, the obtained adsorbent has good reusability and the absorbability decreased only from 98.76 to 94.75% after five cycles. Besides, the adsorption isotherms fitted well to the Langmuir isotherm model and adsorption kinetics followed the pseudo-second-order model. The removal mechanism of mercury via phosphinic acid-functionalized silica nanoparticles was chelation interaction. All the experimental data indicated that the phosphinic acid-functionalized silica nanoparticles are very promising in removal of mercury ions from aqueous solutions.

Mercury removal is an integral part of gas-processing and coal combustion plants due to its implication on health, environment and process equipment. Utilization of impregnated carbons and metal sulfide-based adsorbents for mercury removal are common, however with limitations in adsorption capacity and life time. Continued efforts to develop porous carbon sorbents with better mercury adsorption capacity and kinetics are evident from the open literature with the recent focus being on solid support ionic liquid (SSIL)-based adsorbents with ionic liquid and chelating agents. However, reports on application of SSILs-based adsorbents for gas-phase mercury removal are not available in the open literature. Toward this objective, the present work attempts to synthesize three different SSILs adsorbents identified as SSIL (porous carbon + IL), SSILM (porous carbon + IL + MPTS), SSILA (porous carbon + IL + APTS–MBT) utilizing ultrasound-induced wet impregnation method. The adsorbents were subjected to characterization utilizing BET, XRD, FT-IR and SEM and were tested for its mercury adsorption capacity. The SSIL sorbents were found to possess higher order of magnitude adsorption capacity as compared to high-surface-area porous carbons and metal sulfide-based porous carbons. The adsorption capacity of the SSILs increased orders of magnitude with increase in adsorption temperature from 30 to 50 °C attributed to the predominance of the chemisorption. Among the three SSIL adsorbents, SSILA was found to exhibit highest equilibrium adsorption capacity of 36.9 mg/g at 50 °C. ΔH°, ΔS° and ΔG° indicate that elemental mercury adsorption on SSILA is a spontaneous and endothermic process.

The feasibility of preparing glass ceramic from chambersite gravity tailings was explored. The crystallization parameters and state of glass ceramic were analyzed by Johnson–Mehl–Avrami and Augis–Bennett equations. The effects of sintering temperature and crystallization duration on bending strength and water absorption of glass ceramic were investigated, while the phase composition, crystal structure, lattice constants and surface topography were characterized. The results indicate the crystallization behavior of chambersite tailings glass ceramic is mainly body crystallization with clinopyroxene as a primary crystalline phase, the activation energy for crystallization (E) is 315.27 kJ/mol, the kinetics parameter for crystallization (k) is $$7.98\times 10^{14}$$ , and the main phase lattice constants of clinopyroxene were $$a=0.97392$$ nm, $$b=0.88521$$ nm, $$c=0.52748$$ nm, $$\beta =107.062{^{\circ }}$$ . At sintering temperature of 890 $$^{\circ }$$ C, pyroxene crystal with tetragonal column structure is formed, the diameter of the crystal is about 0.05–0.5 $$\upmu $$ m, while the crystallinity is more than 75%; the bending strength of the glass ceramic increases with the decrease in material particle size; at the $$\hbox {D}_{90}$$ of 5.71 $$\upmu $$ m and crystallization duration of 150 min, the bending strength of glass ceramic reaches the maximum of 128.3 MPa and the water absorption is between 0.06 and 0.02%.

The removal of $$\hbox {H}_{2}\hbox {S}$$ from copper smelting contaminated acid using sodium hydroxide (NaOH) as absorbent was investigated in a RPB reactor. The influences of operating parameters were assessed on the removal efficiency of $$\hbox {H}_{2}\hbox {S}$$ (E) and overall volumetric gas side mass transfer coefficient ( $$K_{\mathrm{G}}a$$ ). The results illustrate that E and $$K_{\mathrm{G}}a$$ increased with increase in high gravity factor, flow rate and concentration of sodium hydroxide while decreased with increase in mass concentration of $$\hbox {H}_{2}\hbox {S}$$ in feed gas. With increase in $$\hbox {H}_{2}\hbox {S}$$ gas flow rate, E was found to decrease while $$K_{\mathrm{G}}a$$ was found to increase. The increase in the temperature of absorption did not show any significant effect on E and $$K_{\mathrm{G}}a$$ . The $$K_{\mathrm{G}}a$$ of the rotating packed bed reactor was about 30 times higher than the conventional packed bed at similar gas liquid throughputs. The superior performance of RBP certainly demands further investigation, process development, scale-up for economical commercial adoption.

This study aimed to assess the utilization of microwave heating for synthesis of rutile TiO2 by employing sulfate titanium slag produced by Panzhihua Iron and Steel Research Institute. To this end, the properties of sulfate titanium slag before and after microwave treatment, i.e., its crystal structure, surface microstructure, and surface chemical functional groups, were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transformation infrared (FT-IR) spectroscopy, respectively. Results of XRD analysis showed that the anosovite phase of the sulfate titanium slag transformed to the rutile TiO2 phase under microwave heating at 1100°C for duration of 120 min. Correspondingly, the SEM images revealed that the surface of the sulfate titanium slag grew as a granular substance after microwave roasting. The granular substance was observed to be rutile TiO2 with a rod-shaped structure. FT-IR spectra demonstrated the occurrence of a blue shift at 472.15 cm−1, indicating phase transformation from anosovite to rutile TiO2 because of the roasting process. From the experimental results, it is concluded that microwave heating can be an effective and efficient approach for the synthesis of synthetic rutile TiO2 from sulfate titanium slag.

The preparation of microsized hematite powder from ferrous sulfate using microwave calcination was investigated based on the TG/DTG curves. The decomposition of industrial ferrous sulfate under air atmosphere was divided into three stages, and a ferrous sulfate sample added with 15% Fe2O3 could strongly absorb microwave energy. Therefore, preparing hematite powder from ferrous sulfate using microwave calcination was feasible. Hematite was obtained under the following optimized conditions: calcination temperature, 850 °C; microwave power, 650 W; and sample amount, 40 g. The obtained hematite satisfied the first-grade quality requirements. The total ferrum value was more than 58%, and the total sulfur and phosphorus contents were less than 0.5% and 0.2%, respectively. X-ray powder diffraction and scanning electron microscopy were used to characterize the structure and morphology of microsized hematite powder. The particles were non-spherical in shape, and the average particle size distribution was 10.45 μm. This work provides new potential applications for waste ferrous sulfate.

Corresponding author designation is missing for Jin Chen in the original publication of this article.

Process optimization of vanadium nitride synthesis from vanadium pentoxide was attempted utilizing microwave carbothermal nitridation at atmospheric pressure using response surface methodology. The process variables that have significant influence on the quality of vanadium nitride such as the reaction temperature, reaction time and carbon addition ratio were investigated. The quadratic models were developed to evaluate the variables and optimize the process conditions, while the analysis of variance was utilized to identify the significant model parameters. The optimum conditions were identified to be a reaction temperature of \({1400^{\circ}{\rm C}}\), reaction time of 240 min and carbon addition ratio of 0.29; the nitride and vanadium content in the vanadium nitride products was found to be 15.83 and 80.99 %, respectively. Experiments were repeated, and the results authenticated the optimized process conditions successfully.

Date palm seed being one of the major waste biomass produced in UAE, is assessed for its potential to be an appropriate precursor for preparation of porous carbon by utilizing KOH as an activating agent through application of process optimization. Process optimization was performed using the popular response surface methodology adopting a Box–Behnken design, to maximize porous carbon BET surface area and % yield, by altering activation temperature, activation time and impregnation ratio. The chemical reactions involved during the impregnation and the carbonization processes for these hydroxide/lignocellulose mixtures present in date palm seed have been proposed. A deep insight has been obtained concerning the possible reactions mechanism. The adsorption capacity was estimated using Iodine adsorption, which infers micropore nature of the porous carbon and it can be utilized for an effective waste water treatment with smaller molecular size substrates.

A new technology is proposed for the production of corundum-mullite refractories. The crystal structures of the raw materials before and after sintering were determined by XRD. An analysis showed that corundum and mullite were mainly crystalline compounds in the sintered samples. The microwave-absorption characteristics of corundum-mullite refractories are optimal when particle size in the refractories is 75 μm.

The technology that waste activated carbon after extracting gold is regenerated with steam under microwave heating was studied. The influence of the activation temperature, activation duration and steam flow rate on iodine adsorption value and regeneration yield of activated carbon was investigated. The response surface methodology (RSM) technique was utilized to optimize the process conditions. The optimum conditions for the preparation of activated carbon are identified to be activation temperature of 831 °C, activation duration of 40 min and steam flow rate of 2.67 mL/min. The optimum conditions result in an activated carbon with an iodine number of 1048 mg/g and a yield of 40%, and the BET surface area evaluated using nitrogen adsorption isotherm is 1493 m2/g, with total pore volume of 1.242 cm3/g. And the pore structure of activated carbon regenerated is mainly composed of micropores and a small amount of mesopores.

The agricultural wastes like date palm seeds to be a suitable precursor for the preparation of porous carbon has been explored in the present work, utilizing phosphoric acid as the activating agent. The experimental methods reported in literature were chosen with certain modification in order to simplify the process. The process optimization was performed using the popular response surface methodology adopting a Box-Behnken design. Process optimization was performed to maximize the porous carbon Brunauer–Emmett–Teller (BET) surface area and the methylene blue (MB) adsorption capacity, with the process variables being the activation temperature, impregnation ratio (IR) and the activation time. The textural characteristics were assessed based on nitrogen adsorption isotherms, scanning electron microscopy, while the adsorption capacity was estimated using the MB adsorption. The optimized experimental conditions were identified to be an activation temperature of 500 °C, IR of 3.1 and activation time of 71.4 min, with the resultant porous carbon having BET surface area of 846.7 m2/g and MB adsorption capacity of 445.7 mg/g. The popular Langmuir and Freundlich adsorption isotherm models were tested, and a maximum monolayer adsorption capacity of the MB was estimated to be 345 mg/g, which compares with the highest of MB reported in literature, evidencing the suitability of the porous carbon for adsorption of macro-molecular compounds.

The central composite process optimization was performed by response surface methodology technique using a design for the treatment of methyltin mercaptide with modified semi-coke. The semi-coke from the coal industry was suitably modified by treating it with phosphoric acid, with a thermal activation process. The objective of the process optimization is to reduce the chemical oxygen demand (COD) and NH4+-N in the methyltin mercaptide industrial effluent. The process variables considered for process optimization are the semi-coke dosage, adsorption time and effluent pH. The optimized process conditions are identified to be a semi-coke dosage of 80 g/L, adsorption time of 90 min and a pH value of 8.34. The ANOVA results indicate that the adsorbent dosage and pH are the significant parameters, while the adsorption time is insignificant, possibly owing to the large range of adsorption time chosen. The textural characteristics of modified semi-coke were analyzed using scanning electron microscopy and nitrogen adsorption isotherm. The average BET surface area of modified semi-coke is estimated to be 915 m2/g, with the average pore volume of 0.71 cm3/g and a average pore diameter of 3.09 nm, with micropore volume contributing to 52.36%.

This paper attempts to capture the difference between the ultrasound augmented and conventional sulphuric acid leaching of zinc from zinc residue, having a Zn content of 12.31 %, along with other metallic compounds such as Fe, Pb and SiO2. The leaching temperature, sulphuric acid concentration, particle size, Liquid/solid ratio and the ultrasound power have been chosen as parameters for investigation. The shrinking core model is utilized for analyzing the rate controlling step in the leaching process. Only a maximum of 67 % of zinc could be leached using conventional process, while 80 % could be leached with the ultrasound augmentation. For both the processes the rate controlling step is identified to be the diffusion through the product layer. The reaction order with respect to the sulphuric acid concentration is found to be 1.33 and 0.94, while the activation energy being are 13.07 and 6.57 kJ/mol, for the conventional and ultrasound-augmented leaching process, respectively. The raw as well as the leached residue are characterized using XRD and SEM/EDS analyses.

The present paper attempts to assess the effects of microwave irradiation on the leachability of refractory gold ores. Characteristics of the crystal structure and microstructure of the ores were determined by x-ray structural analysis (XRD) and scanning electron microscopy (SEM) before and after microwave irradiation. Compared to conventional processes, microwave leaching processes are highly energy-efficient, take less time, and do not harm the environment. The experimental results show that the amount of gold extracted increases with microwave leaching temperature. The results demonstrate that microwave irradiation techniques can be applied effectively and efficiently to the leaching of refractory gold ores.

This study relates to optimization of process conditions for sulfur impregnation process on to a virgin steam-activated commercial carbon, with the objective of maximizing the mercuric chloride adsorption. Process optimization was performed using response surface methodology adopting Box–Behnken design. The chosen key process parameters being impregnation temperature (IT), carbon to sulfur ratio (CSR), and impregnation time (ITE), with lower and upper bounds for process conditions being 250–600 °C IT, 0.5–4 CSR, and 15–45 min ITE. The optimum conditions were identified to be an IT of 544 °C, CSR of 0.53 and ITE of 43 min with the HgCl2 adsorption capacity of 85 mg/g. The optimized process conditions were further ensured with repeat runs with reproducible results within acceptable variation. Langmuir and Freundlich equilibrium adsorption isotherm models fitted well with the experimental data. The maximum monolayer adsorption capacity was found to be 294 mg/g which was quite high as compared with the maximum reported in literature. Further, the SEM–EDX analysis evidence the higher amount of sulfur and uniform distribution of sulfur over the surface of activated carbon.

Date palm being one of the major biomass sources, largely being cultivated in UAE, is assessed for its potential to be an appropriate precursor for preparation of porous carbon. Porous carbon is prepared using the date palm pits in a tubular furnace with CO2 as the activating agent assessing the effect of process variables activation temperature, activation time and CO2 flow rate. Process optimization is performed to identify the process conditions that maximize the yield and BET surface area of the porous carbon using surface response methodology (RSM) based on central composite design (CCD). The influence of process parameters on the properties of porous carbon is investigated using analysis of variance (ANOVA) to identify the significant parameters. The optimum conditions for the preparation of porous carbon has been identified to be an activation temperature of 971°C, activation time of 56 min and CO2 flow rate of 5.1 cc/min based on the maximizing the yield and BET surface area. The optimum yield and BET surface area has been predicted to be 14.8% and 666 m2/g using the process optimization software. The textural characteristic of the optimized sample using nitrogen adsorption isotherm show the carbon to be predominantly microporous with the mean pore diameter estimated to be 1.76 nm using NLDFT method.

The present work is an attempt to compile and analyze the literature pertaining to catalytic vapor phase pyridine synthesis. In the beginning pyridine deriving from coal tar and subsequent years it was developed as catalytic vapor phase synthesis using acetaldehyde, formaldehyde and ammonia provides best prospect for the growing demand. HZSM-5 is the best catalyst present in market to for catalytic pyridine bases; it has unique structural and acidity properties over other catalysts. It is probable that the reactants are adsorbed at catalytic sites, formation of imines precedes cyclisation and desorption from catalytic pores. In this review detail summary of the inventions in chronological order and with their postulates is narrated.

An extensive experimental study has been attempted to assess the effect of heating method and the activation agent on the pore characteristics of activated carbon from coconut shell. The results show that the textural characteristics of activated carbon improve with increase in holding time until an optimum, while the yield decrease with an increase in the holding time, using conventional activation method. The microwave heating requires significantly lesser holding time as compared to conventional heating method, to produce activated carbon of comparable quality, with higher yield. The BET surface area of steam activated carbon using microwave heating is significantly higher than the conventional heating, however with CO2 activation microwave heating shows only a marginal increase in BET surface area as compared to conventional heating. The activated carbon prepared using microwave heating has a surface area of 1,684 m2/g with steam activation, while CO2 activation has a surface area of 1,716 m2/g, which is significantly higher than the majority of the surface area reported in literature using conventional physical activation.

Fluidized bed drying kinetics of highly porous material which offers free flow of moisture to surface of the material is modeled utilizing the simplified bubbling bed model. The simplification step utilizes estimation of the overall transfer resistance, by summing all the resistances from the bubble phase to the emulsion phase. The model predictions are compared with the published experimental data covering the operating variables such as the inlet air temperature, the air flow rate, material characteristics and are found to match satisfactorily. The model highlights the importance of bubble size estimation, as it largely dictates the drying kinetics.

The microwave absorbing characteristics of basic cobalt carbonate, cobalt oxide (Co3O4), and the mixture of basic cobalt carbonate and cobalt oxide were investigated by means of microwave cavity perturbation, their temperature increasing curves were measured, and their ability to absorb microwave energy was also assessed based on the temperature increasing behavior of the material exposed to microwave field. Analyses of spectrum attenuation and relative frequency shift show that basic cobalt carbonate has weak capability to absorb microwave energy, while cobalt oxide has very strong capability to absorb microwave energy. It is feasible to thermally decompose basic cobalt carbonate though addition of small amount of cobalt oxide in microwave fields. The capability to absorb microwave energy of sample increases with an increase in mixing ratio of Co3O4.