Cadmium ions pollution and waste resulting from industrial activities are classified as serious environmental problems. In this study, we performed comparative adsorption studies of cadmium (II) on ...phosphogypsum (PG) and natural clay (NC) from an aqueous solution. The difference in adsorption mechanisms between phosphogypsum and natural clay was inspected using scanning electron micrographs; X-ray diffraction and Fourier transform infrared. The effects of contact time and certain factors such as the adsorbent dosage and the pH of the solution were studied. The comparative study shows that the differences in adsorption behavior come from the chemical and structural differences of the adsorbents studied. It was found that 0.73 mg·g−1 is the maximum adsorption capacity for phosphogypsum, whereas for natural clay it was 5.65 mg·g−1. Cadmium (II) removal was pH-dependent and the optimum adsorptions of phosphogypsum and clay were found at pH basic. It has been confirmed that the pseudo-second order model is best suited to the kinetics of the process studied for the two adsorbents. Overall, natural clay is a better adsorbent than phosphogypsum and this latter can be used as a potential adsorbent candidate for the removal of Cd(II) from aqueous solutions.
Soil organic carbon (SOC) is one of the central issues in dealing with soil fertility as well as environmental and food safety. Due to the lack of relevant data sources and methodologies, analyzing ...SOC dynamics has been a challenge in Morocco. During the last two decades, process-based models have been adopted as alternative and powerful tools for modeling SOC dynamics; whereas, information and knowledge on the most sensitive model inputs under different climate, and soil conditions are still very limited. For this purpose, a sensitivity analysis was conducted in the present work, using the DeNitrification-DeComposition (DNDC) model based on the data collected at a semi-arid region (Merchouch station, Morocco). The objective is to identify the most influential factors affecting the DNDC-modeled SOC dynamics in a semi-arid region across different climatic and soil conditions. The results of sensitivity analysis highlighted air temperature as the main determinant of SOC. A decrease in air temperature of 4 °C results in an almost 161 kg C ha−1 yr−1 increase in C sequestration rate. Initial SOC was also confirmed to be one of the most sensitive parameters for SOC. There was a 96 kg C ha−1 yr−1 increase in C sequestration rate under low initial SOC (0.005 kg C ha−1). In the DNDC, air temperature in climatic factors and initial SOC in variable soil properties had the largest impacts on SOC accumulation in Merchouch station. We can conclude that the sensitivity analysis conducted in this study within the DNDC can contribute to provide a scientific evidence of uncertainties of the selected inputs variables who can lead to uncertainties on the SOC in the study site. The information in this paper can be helpful for scientists and policy makers, who are dealing with regions of similar environmental conditions as Merchouch Station, by identifying alternative scenarios of soil carbon sequestration.
This work aims at developing a dynamic layer crystallizer operated batchwise, for freezing desalination of sea water. The experiments were performed with water/NaCl solutions and with samples of sea ...water from Nice, Rabat and Marseille. The pilot crystallizer consists of a cooled tube immersed in a cylindrical double jacketed tank. The solution is poured into the tank and the crystallization takes place on the external surface of the tube, by applying a cooling ramp in the tube. The solution is agitated by air bubbling. The whole process involves the freezing step, leading to the crystallization of the ice layer and the sweating step, which consists of purifying in depth the ice layer by melting the impure zones. A parametric study on the effect of the operating parameters has allowed quantifying the role of the different key parameters of the freezing and sweating steps. Three experiments allowed reaching salinities lower than 0.5g/kg, satisfying the standards of drinking water. The duration of the whole process dropped to only 8h (5h for freezing and 3h for sweating), with a yield of sweating equal to about 50%, provided severe conditions were applied for sweating. Higher yields required longer times. Overall, the results show the feasibility of the technique.
► Initial temperature, ice growth rate and solution salinity are the parameters affecting ice purity. ► The sweating step is able to efficiently complete the purification. ► The duration of the whole process dropped to only 8h (5h for freezing and 3h for sweating).
Experimental setup for fixed-bed batch adsorption on activated carbon.
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•Illite and Attapulgite natural clays are mostly insolubles and stables in the wet phosphoric acid due to their ...high quartz content.•The Montmorillonite is predominantly soluble in the wet phosphoric acid.•Lead has shown a total removal by adosprtion in both natural and activated clays.•Cadmium is not removed by adsorption on both naturals and activated clays.•Chromium is partially adsorbed on clays.•The chemical activation of clays at pH of 1 shows a significant adsorption of Arsenic and Chromium.•Sulfur-impregnated activated carbon (SAC) does not show any potential adsorption of metals.
Cadmium and trace metals elements present a significant challenge to the fertilizer industry, considering the increasingly strict regulation on their contents in fertilizers. Consequently, a specific need to develop efficient and cost-effective technologies for their removal has appeared within the last few years. This research article focuses on the adsorption technology already proved for water treatment as a promising and emerging technology for removing cadmium and trace metals from wet phosphoric (WPA), given its ease of use and low cost. Literature highlights a lack of adsorption applications for treating WPA in industrial conditions in terms of P2O5 content and temperature. In this scope, effective natural and activated clays, Montmorillonite (M), Illite (I), and Attapulgite (A), as well as sulfur-impregnated activated carbon, were prepared, characterized, and used for the adsorption of cadmium and trace metals from WPA with 25 % (w/w) P2O5 at 80 °C. For clay adsorbents, different quantities of 1, 2, 3, and 4 % (w/w) were tested with a contact time of 30 min. As a result, it was found that lead was removed in total while there was no significant adsorption of cadmium and nickel. Slight adsorption efficiency of 20 % was registered for chromium and arsenic, equivalent to an adsorption capacities of 2.5 mg/g and 0.2 mg/g, respectively. The latter effect could be attributed to their multiple oxidation states. The chemical activation of clays to pH 1 by using a 5 M NaOH solution increased chromium and arsenic adsorption efficiencies to 46 % and 19 %, equivalent to an adsorption capacities of 0.2 mg/g and 3.7 mg/g, respectively. Adsorption could not be reached for sulfur-impregnated activated carbon despite its large specific surface (528 m2/g) and its sulfur impregnation (10 % w/w). This latter was supposed to activate the chemisorption of cadmium and other trace metals like arsenic, copper, and zinc by forming covalent bonds due to their chemical affinity to sulfur. However, research on the carbon structure showed that sulfur was inactive as it forms a covalent bond with carbon in the mineral structure of activated carbon.
In the process of desalination by indirect freezing, ice formed on the cooled surface contains impurities due to kinetic effects. Sweating is an efficient method by which ice layer is purified under ...the effect of temperature gradient. The main kinetic parameters influencing sweating of ice are initial concentration of ice, sweating temperature and sweating time. In the present work, the effects of these parameters were studied using an experimental design. A statistical model for ice weight and ice purity was developed. The graphical representation of this model in the space of the variables enabled optimization of the whole desalination process time, which led to ice salinity less than the drinking water standards (0.5g/kg).
►Layer melt crystallization was applied to seawater desalination. ►The process involves two consecutives steps: freezing and sweating. ►Sweating has enabled the obtention of ice with low salt concentration, satisfying standards of potability. ►Optimal operating conditions are proposed by means of an experimental design.
•High ligands excess is required for effective cadmium removal from WPA.•DIBDPi, DEDTP, ZDDP, TBAI, Na2CS3 and Aliquat 366 remove cadmium from WPA.•DIBDPi, DEDTP and ZDDP are distinctly effective and ...efficient.•DIBDTPi is the most proved and effective ligand for cadmium removal from WPA.
Recently, the application of organic coordination ligands for the cadmium removal from wet phosphoric acid (WPA) has shown a great interest, and a certain number of commercially available ligands have shown some affinity and selectivity for cadmium. This technic consists in making complexes between cadmium and ligands. It is easy to integrate industrially and does not require significant investment and maintenance overhead; the cost is driven by the organic ligand stability, efficiency and price. However, the challenge still the high cost of ligand and its insufficient world production capacity in comparison to the increasingly demand. The present research article aims to experiment new organic ligands potentially proved in various media for the cadmium removal. The cadmium removal tests from WPA were carried out under the industrial conditions of 25 % (w/w) P2O5, 14 ppm Cd, and 80 °C. A number of 21 organic ligands were carefully selected based on their potential removal of cadmium. The tests were separately performed under the stoichiometric conditions corresponding to a molar ratio R (nLigand/ncd) of 2, and the excess conditions corresponding to a molar ratio R (nLigand/ncd) of 10. Distinctly, the results relatively to R equaling 10 showed significant increase in cadmium removal specifically to DIBDPi (Diisobutyl dithiophosphinate), DEDTP (Diethyl dithiophosphate), ZDDP (Zinc dialkyl dithiophosphinate), TBAI (Tetrabutyl ammonium iodide), Na2CS3 (Sodium trithiocarbonate), and Aliquat 366 (Methyltrioctyl ammonium chloride), with an efficiency of 86 %, 71 %, 68 %, 29 %, 24 %, and 21 %, respectively. The other ligands still showed no affinity for cadmium removal from WPA.
Mesoporous hybrid silica bearing zwitterionic species were synthesized via template-directed hydrolysis-polycondensation reactions from zwitterionic ammonium sulfonate precursors. The formation of ...the nanostructured phases involves specific precursor-template interactions. The obtained materials are efficient heterogeneous catalysts in Biginelli reactions.
Abstract
A hybrid system proposed by three different specifications for the equipment of a tourist lodge in the headland of south-west Morocco was sized by analysing the limits of load profile ...constraints, such as hour-to-hour variability (HHR), day-to-day variability (DDR) and the operating reserve rate (ROR). Based on the three-factor Doehlert matrix recommendations, the simulations employed an energy-sizing tool for hybrid renewable-energy systems. Testing was conducted with DDR at 5–30%, HHR at 10–30% and ROR at 0–20%. Under these conditions, a second-order polynomial relationship with a correlation rate of ~90% was found between the net present cost (NPC) of the system, the levelized cost of electricity and the various constraint factors. The first specification, SPC(1), composed of generators and batteries, was introduced to control and validate the simulation independently of renewable energy, which showed a positive manifestation with the imposed constraints. The analysis expanded by introducing solar and wind energy resources. The SPC(2) configuration added PV modules to the SPC(1) and the SPC(3) configuration added wind turbines to SPC(2). The effect of DDR, HHR and ROR in the trials was significant by linear regression. At the same time, only DDR had a significant quadratic regression. The others, with their pairwise interactions, were insignificant. The desirability procedure made it possible to calculate the maximum limits of load profile constraint variables leading to targets of LCOE = 0.41 US$/kWh and NPC = US$320 080.1 of the load profile constraints: the DDR = 15.47% and the HHR = 26.55% at an ROR rate of 17.77%.
•Cadmium is a serious challenge to the fertilizers industry.•There are sustainability challenges in terms of economy, environment protection, and integration of cadmium removal technologies at the ...industrial scale that are investigated.•It is tried to explore the importance of Cd removal from the fertilizer solutions, investigate on different methods of treatment, reveal the advantages and disadvantages of each one and talk about what is going on the phosphate fertilizer industry in general.
The fertilizers industry is mainly developing its activities by processing phosphate, phosphoric acid and ammonia. The cadmium (Cd) is one of the most challenging materials, which is existed naturally in the heterogeneous mixture of phosphate ore as the main source of phosphate (feed of fertilizer production). The legal limits for cadmium in fertilizers is 60 mg/kg in different regions, guidelines and standards such as European Union (EU), China, Canada, and International Fertilizer Association (IFA). Therefore, the cadmium removal from wet phosphoric acid that is produced from the Wet Process Acid (WPA) is today a massive challenge to the fertilizers industry to face environmental, economic, financial, political and other legal constraints. These constraints have committed to develop significant research and innovation interests on cadmium removal technologies from the phosphate ore as feedstock and the produced phosphoric acid. The research reported in the present article aims to give a comprehensive overview and relevant developments of cadmium removal technologies in phosphoric acid industry, with a specific focus on technical feasibility, complexity, cost evaluation and sustainability of the main technologies that could present a potential application at the industrial scale.
The phosphogypsum (PG) is a waste by-product of the wet process of phosphoric acid production. In this study, phosphogypsum was prepared and used as an adsorbent for the removal of cadmium, copper, ...and zinc ions from aqueous solutions. First, the phosphogypsum was characterized, before and after the adsorption process, by Fourier transform infrared spectroscopy and scanning electron microscopy. Then the effect of the initial pH of the metal ions solutions on the adsorption process has been studied. Second, the competitive adsorption of metal ions on phosphogypsum in the ternary mixture was investigated and compared with non-competitive adsorption. The results show that the adsorption of metal ions by phosphogypsum depends on the solution pH. The selectivity order of the adsorbent is Cd2+ > Cu2+ > Zn2+. From these results, it can be concluded that the phosphogypsum could be a low-cost material for heavy metals removal, especially cadmium ion, from aqueous basic solutions.
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