الملخص: Wastewater generated from phosphoric acid industry poses a real environmental challenge. This water contains valuable components the utilization of which can contribute to the conservation of natural resources. Water sample from an effluent pond of a phosphoric acid plant was collected and characterized for its physical and chemical properties. The collected samples were subjected to a hybrid process of chemical precipitation followed by nanofiltration. Both sulphate and fluoride ions were separated by precipitation using Ca(OH)2. Silicon exhibited complex behaviour during the precipitation stage. The observed flux using the different tested membranes (NF90, NF270, and BW30) indicated the success of the pre-treatment method in preventing heavy fouling. Very high rejections were obtained using the NF90 and BW30 membranes and, generally, the rejection increased with pressure. As expected, higher flux and lower rejections were observed with NF270 for Si and H3PO4 species. At a pressure of 20 bar the rejection increased with feed concentration which can be attributed to Donnan effects. It is concluded that NF270 could be potentially applied to separate PA from the rest of the species present in water. However, the main challenge is the low rejection of Si.

الملخص: Reaction and activation energy barriers are calculated for the H abstraction reactions (C6H5SH + X• → C6H5S + XH, X = H, OH and HO2) at the BB1K/GTLarge level of theory. The corresponding reactions with H2S and CH3SH are also investigated using the G3B3 and CBS-QB3 methods in order to demonstrate the accuracy of BB1K functional in finding activation barriers for hydrogen atom transfer reactions. Arrhenius parameters for the title reactions are fitted in the temperature range of 300 K–2000 K. The calculated reaction enthalpies are in good agreement with their corresponding experimental reaction enthalpies. It is found that H abstraction by OH radicals from the thiophenol molecule proceed in a much slower rate in reference to the analogous phenol molecule. ΔfHo298 of thiophenoxy radical is calculated to be 63.3 kcal/mol. Kinetic parameters presented herein should be useful in describing the decomposition rate of thiophenol; i.e., one of the major aromatic sulfur carriers, at high temperatures.

الملخص: The aim of this paper was to study the effect of tribenzylamine and pyridine on the kinetics of the hydrolysis reaction of benzoyl chloride in water-dioxane solution. The benzoyl chloride and water initial concentrations were 0.005 and 1 mol/L, respectively. While, the initial concentrations of pyridine and tribenzylamine varied in the range of 0.005-0.02 mol/L and 0.007-0.014 mol/L, respectively. It was found that the addition of tribenzylamine to benzoyl chloride hydrolysis reaction has no catalytic effect and hence the rate constant can be calculated using a first-order rate equation. In the presence of pyridine, reaction obeyed second-order rate. The relationship between the reaction rate constant and pyridine initial concentration was found to be linear with a rate constant of 0.752 × 10–3 min–1.

الملخص: Unlike the chemistry underlying the self‐coupling of phenoxy (C6H5O) radicals, there are very limited kinetics data at elevated temperatures for the reaction of the phenoxy radical with other species. In this study, we investigate the addition reactions of O2, OH, and NO2 to the phenoxy radical. The formation of a phenoxy‐peroxy is found to be very slow with a rate constant fitted to k = 1.31 × 10−20T2.49 exp (−9300/T) cm3/mol/s in the temperature range of (298–2,000 K) where the addition occurs predominantly at the ortho site. Our rate constant is in line with the consensus of opinions in the literature pointing to the observation of no discernible reaction between the oxygen molecule and the resonance‐stabilized phenoxy radical. Addition of OH at the ortho and para sites of the phenoxy radical is found to afford adducts with sizable well depths of 59.8 and 56.0 kcal/mol, respectively. The phenoxy‐NO2 bonds are found to be among the weakest known phenoxy‐radical bonds (1.7–8.7 kcal/mol). OH‐ and O2‐initiated mechanisms for the degradation of atmospheric phenoxy appear to be negligible and the fate of atmospheric phenoxy is found to be controlled by its reaction with NO2

الملخص: Adsorption of SO2 onto Jordanian zeolitic tuff (ZT) was examined in this work. ZT samples were characterized by XRD, XRF, BET and TGA analyses. The sorption process was carried out in a fixed bed column at different operating conditions. The unique measuring technique, namely UIC sulfur coulometer, for SO2 measurement was adopted in this work. Uptake of SO2 by ZT was found to increase with increasing temperature up to a temperature of 200 °C and then decrease at higher temperatures. It was also found that drying of ZT, by conventional and microwave heating has a considerable effect on SO2 uptake and breakthrough time. Experimental data for adsorption isotherms were obtained and found to follow the BET isotherm model. It was found that the adsorption process is exothermic in nature. Thermal pre-treatment was found to affect the adsorption capacity and breakthrough time of ZT. The maximum adsorption capacity was obtained after thermal pretreatment of ZT at a temperature of 200 °C, which could be linked to the effect of heating on the destruction of crystal structure of phillipsite, the crystal refinement of chabazite, and the formation of new aluminosilicate crystalline phases. ZT can be regenerated and the initial adsorption capacity was preserved after three regeneration cycles.

الملخص: A wide variety of semi-volatile organic chemicals (SVOCs) are still in use in agricultural practices. A proper understanding of the environmental fate and ecotoxicological risk associated with these compounds can aid decision making, particularly regarding product registration and licensing. The aim of this paper is to expand the use of a previously developed Multimedia Agricultural Fate and Risk Assessment Model (MAFRAM) to SVOCs by adopting the fugacity concept as a second criterion to the existing MAFRAM partitioning criterion (i.e., aquivalence). Volatilization processes from surface compartments into the atmosphere were also included. For example, the application of the generalized model was illustrated using an average annual application rate of 4.48 kg/ha of chlorpyrifos over a typical homogeneous region. Chlorpyrifos emissions were assumed to take place in three environmental compartments (i.e., soil, air, and aboveground plants) with fractions of 0.1, 0.3, and 0.6, respectively. The trends seen in the modeling results were in good agreement with the existing experimental data. Validation issues in MAFRAM were also discussed. Comprehensive experimental validation is unattainable because of the large scale of the areas covered, the lack of boundaries for the system considered, and the uncertainty in the input parameters.

الملخص: Oil shale combustion is a promising option for Jordanian oil shale utilization. Restrictions on the exploitation and utilization of this resource are partly due to the high sulfur content of the oil shale, which leads to production of large quantities of sulfur dioxide during combustion. Mitigation of sulfur dioxide prior effluent gas release is important for maintaining air quality and preventing several environmental problems, e.g. acid rain. A number of effluent gas desulfurization techniques are available. These can be broadly classified into four categories: absorption of SO2 in liquids, absorption by moist particles, gas phase conversion of SO2, and sorption by solids. Solid-phase sorption has been examined in this study for SO2 removal during oil shale combustion using Jordanian zeolitic tuff

الملخص: The reaction of aniline with hydrogen atom is investigated herein using the hybrid meta-DFT functional of BB1 K. Hydrogen atom is found to preferentially add at an ortho position. However, the fate of the o-(C6H5NH2)H adduct is found to be solely the deactivation of the initial addition channel. The rate constant for the abstraction channel (C6H5NH2 + H → C6H5NH + H2) is fitted by the expression 1.10 × 10−11 exp(−4,200/T) cm3 molecule−1 s−1. Our calculated rate constant for the abstraction channel agrees very well with the available experimental measurements. Satisfactory agreement is found between calculated and experimental measurements for the displacement channel (C6H5NH2 + H → C6H6 + NH2). Our detailed analysis for the corresponding displacements in toluene and phenol suggests that the three systems exhibit similar behavior with regard to the relative importance of abstraction and displacement channels.

الملخص: The effluent ponds from phosphoric acid and fertilizer industries are a worldwide problem. Wastewater in these ponds contains high concentration of acids and heavy metals that seriously contaminates the environment and underground water. On the other hand, it contains valuable components such as phosphoric acid, fluorine and flousilicic acid. In this work, wastewater samples from effluent pond of the Indo Jordan Chemicals (IJC) plant were collected. These samples were characterized for their pH, and chemical composition. The pH of pond water was found to be about 0.8 due to its high content of HF, H2SiF6 and H3PO4. Potentiometric titration, chloride and fluoride ion selective electrodes and other acid base titration methods were employed to determine the content of the above acids. AAS was also used to determine the content of heavy metals in this waste water. Potentiometric titration curves were produced to determine the optimum neutralization conditions for several synthetic mixtures made from the above acids, and for real effluent wastewater. XRD, XRF and SEM analyses were employed for analysis of the products of calcium hydroxide neutralizations. It was found that fluorine is present in effluent pond water in two forms: HF and H2SiF6. Precipitation experiments revealed that the reaction of H2SiF6 with Ca(OH)2 yielded only CaF2 with no CaSiF6. Furthermore, it was found that it is possible to separate sulfate in an initial precipitation stage. Additionally, it is possible to remove almost all fluoride in the form of CaF2 leaving at least 60% of H3PO4 in water. Amorphous silica could be removed by aging the solution after fluoride removal.

الملخص: Oil shale in Jordan and elsewhere faces many obstacles that hinder its utilisation. Recent developments of the utilization of Jordanian oil shale include the establishment of power generation companies that depend on the technology of atmospheric fluidized bed combustion systems (FBC). Sintering is believed to have been the main cause of many operational problems of FBC systems. This work investigates the sintering propensity of ash obtained from oil shale from Jordania’s largest oil shale deposit El-Lajjun, when combusted at different temperatures, as well as major mineral transformations as a function of temperature. The results obtained by the pressure drop sintering technique showed that the sintering temperature is a strong function of the combustion temperature. Two regions of sintering were found: a low temperature sintering region and a high sintering temperature region. The low sintering temperature region starts at around 700 °C where it is believed to be due to the sintering of limestone. On the other hand, the high sintering temperature region, which starts at 900 °C, is believed to be due to the sintering of the wollastonite formed. Scanning Electron Microscope (SEM) images and Brunauer–Emmett–Telle (BET) measurements confirm these findings

الملخص: The main object of this study was to study the effect of pyridine, 2-methyl pyridine, 3-methyl pyridine, 2,6-dimethyl pyridine, quinoline and tribenzylamine on the hydrolysis kinetics of benzoyl chloride in water-dioxane solutions. The investigation has been made by means of gas-liquid chromatography measurements. Almost equal rate constants have been determined for the hydrolysis reaction of benzoyl chloride in dioxane solutions. The catalytic effect of the studied range of tertiary amines on the hydrolysis reaction of benzoyl chloride was determined

الملخص: The purpose of the study is to investigate the optimum conditions for the precipitation of sodium hexafluorosilicate (Na2SiF6) from waste hexafluorosilicic acid, an effluent from the phosphoric acid industry. Sodium chloride and sodium hydroxide were used as reactants to produce Na2SiF6. The effect of various parameters on the precipitation was investigated and includes; the molar ratio of the reactants, contact time, the temperature and the effect of seeding.The optimum reaction conditions were found to be as follows; excess sodium chloride or sodium hydroxide to hexafluorosilicic acid of 25%, contact time 40 minutes and a reaction temperature of 40°C.The reaction of hexafluorosilicic acid with an aqueous solution of sodium chloride at optimum conditions gave a maximum yield of 94.26% Na2SiF6 while the reaction of hexafluorosilicic acid with the aqueous solution of sodium hydroxide at optimum conditions gave a maximum yield of 97.3% Na2SiF6. The X-Ray diffraction (XRD) analysis reveals that the only crystals present in the precipitate are Na2SiF6. Also, Scanning Electron Microscope (SEM) analysis shows that the different morphology of these crystals depend on the precipitation conditions

الملخص: The main goal of this paper was to introduce an environmental fate and risk assessment methodology for comparing and establishing the general features of new and existing non-volatile organic chemicals (NVOCs) used in agricultural activities, based on simple and readily available properties. This methodology is a computer program called the multimedia agricultural fate and risk assessment model (MAFRAM). This model is a combination of the EQC-2V model, which describes the fate of NVOCs, with the ecological relative risk (EcoRR) approach, which assesses the ecotoxicological risk to agro-ecosystems. MAFRAM divides the agricultural environment into two main zones, which are the on- and off-farm zones. Each zone is subdivided into six compartments, including the air, water, soil, sediment, aboveground plants, and roots. The required input data are the chemical–physical properties of the pesticide, biota data, and environmental properties. The MAFRAM output includes the inter-compartmental transport and transfer rates, the primary loss mechanisms, chemical concentration, amount, residence time, and the rank of risk in each compartment. In addition, it can provide several secondary results. The MAFRAM application was illustrated using typical homogenous region properties and was run with an illustrative emission rate of 1 kg/h into air, using spinosad as a case study.

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الملخص: Wastewater generated from phosphoric acid industry poses a real environmental challenge. This water contains valuable components the utilization of which can contribute to the conservation of natural resources. Water sample from an effluent pond of a phosphoric acid plant was collected and characterized for its physical and chemical properties. The collected samples were subjected to a hybrid process of chemical precipitation followed by nanofiltration. Both sulphate and fluoride ions were separated by precipitation using Ca(OH)2. Silicon exhibited complex behaviour during the precipitation stage. The observed flux using the different tested membranes (NF90, NF270, and BW30) indicated the success of the pre-treatment method in preventing heavy fouling. Very high rejections were obtained using the NF90 and BW30 membranes and, generally, the rejection increased with pressure. As expected, higher flux and lower rejections were observed with NF270 for Si and H3PO4 species. At a pressure of 20 bar the rejection increased with feed concentration which can be attributed to Donnan effects. It is concluded that NF270 could be potentially applied to separate PA from the rest of the species present in water. However, the main challenge is the low rejection of Si.

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الملخص: The aim of this paper was to study the effect of tribenzylamine and pyridine on the kinetics of the hydrolysis reaction of benzoyl chloride in water-dioxane solution. The benzoyl chloride and water initial concentrations were 0.005 and 1 mol/L, respectively. While, the initial concentrations of pyridine and tribenzylamine varied in the range of 0.005-0.02 mol/L and 0.007-0.014 mol/L, respectively. It was found that the addition of tribenzylamine to benzoyl chloride hydrolysis reaction has no catalytic effect and hence the rate constant can be calculated using a first-order rate equation. In the presence of pyridine, reaction obeyed second-order rate. The relationship between the reaction rate constant and pyridine initial concentration was found to be linear with a rate constant of 0.752 × 10–3 min–1.

الملخص: Reaction and activation energy barriers are calculated for the H abstraction reactions (C6H5SH + X• → C6H5S + XH, X = H, OH and HO2) at the BB1K/GTLarge level of theory. The corresponding reactions with H2S and CH3SH are also investigated using the G3B3 and CBS-QB3 methods in order to demonstrate the accuracy of BB1K functional in finding activation barriers for hydrogen atom transfer reactions. Arrhenius parameters for the title reactions are fitted in the temperature range of 300 K–2000 K. The calculated reaction enthalpies are in good agreement with their corresponding experimental reaction enthalpies. It is found that H abstraction by OH radicals from the thiophenol molecule proceed in a much slower rate in reference to the analogous phenol molecule. ΔfHo298 of thiophenoxy radical is calculated to be 63.3 kcal/mol. Kinetic parameters presented herein should be useful in describing the decomposition rate of thiophenol; i.e., one of the major aromatic sulfur carriers, at high temperatures.

الملخص: Unlike the chemistry underlying the self‐coupling of phenoxy (C6H5O) radicals, there are very limited kinetics data at elevated temperatures for the reaction of the phenoxy radical with other species. In this study, we investigate the addition reactions of O2, OH, and NO2 to the phenoxy radical. The formation of a phenoxy‐peroxy is found to be very slow with a rate constant fitted to k = 1.31 × 10−20T2.49 exp (−9300/T) cm3/mol/s in the temperature range of (298–2,000 K) where the addition occurs predominantly at the ortho site. Our rate constant is in line with the consensus of opinions in the literature pointing to the observation of no discernible reaction between the oxygen molecule and the resonance‐stabilized phenoxy radical. Addition of OH at the ortho and para sites of the phenoxy radical is found to afford adducts with sizable well depths of 59.8 and 56.0 kcal/mol, respectively. The phenoxy‐NO2 bonds are found to be among the weakest known phenoxy‐radical bonds (1.7–8.7 kcal/mol). OH‐ and O2‐initiated mechanisms for the degradation of atmospheric phenoxy appear to be negligible and the fate of atmospheric phenoxy is found to be controlled by its reaction with NO2

الملخص: Adsorption of SO2 onto Jordanian zeolitic tuff (ZT) was examined in this work. ZT samples were characterized by XRD, XRF, BET and TGA analyses. The sorption process was carried out in a fixed bed column at different operating conditions. The unique measuring technique, namely UIC sulfur coulometer, for SO2 measurement was adopted in this work. Uptake of SO2 by ZT was found to increase with increasing temperature up to a temperature of 200 °C and then decrease at higher temperatures. It was also found that drying of ZT, by conventional and microwave heating has a considerable effect on SO2 uptake and breakthrough time. Experimental data for adsorption isotherms were obtained and found to follow the BET isotherm model. It was found that the adsorption process is exothermic in nature. Thermal pre-treatment was found to affect the adsorption capacity and breakthrough time of ZT. The maximum adsorption capacity was obtained after thermal pretreatment of ZT at a temperature of 200 °C, which could be linked to the effect of heating on the destruction of crystal structure of phillipsite, the crystal refinement of chabazite, and the formation of new aluminosilicate crystalline phases. ZT can be regenerated and the initial adsorption capacity was preserved after three regeneration cycles.

الملخص: A wide variety of semi-volatile organic chemicals (SVOCs) are still in use in agricultural practices. A proper understanding of the environmental fate and ecotoxicological risk associated with these compounds can aid decision making, particularly regarding product registration and licensing. The aim of this paper is to expand the use of a previously developed Multimedia Agricultural Fate and Risk Assessment Model (MAFRAM) to SVOCs by adopting the fugacity concept as a second criterion to the existing MAFRAM partitioning criterion (i.e., aquivalence). Volatilization processes from surface compartments into the atmosphere were also included. For example, the application of the generalized model was illustrated using an average annual application rate of 4.48 kg/ha of chlorpyrifos over a typical homogeneous region. Chlorpyrifos emissions were assumed to take place in three environmental compartments (i.e., soil, air, and aboveground plants) with fractions of 0.1, 0.3, and 0.6, respectively. The trends seen in the modeling results were in good agreement with the existing experimental data. Validation issues in MAFRAM were also discussed. Comprehensive experimental validation is unattainable because of the large scale of the areas covered, the lack of boundaries for the system considered, and the uncertainty in the input parameters.

الملخص: Oil shale combustion is a promising option for Jordanian oil shale utilization. Restrictions on the exploitation and utilization of this resource are partly due to the high sulfur content of the oil shale, which leads to production of large quantities of sulfur dioxide during combustion. Mitigation of sulfur dioxide prior effluent gas release is important for maintaining air quality and preventing several environmental problems, e.g. acid rain. A number of effluent gas desulfurization techniques are available. These can be broadly classified into four categories: absorption of SO2 in liquids, absorption by moist particles, gas phase conversion of SO2, and sorption by solids. Solid-phase sorption has been examined in this study for SO2 removal during oil shale combustion using Jordanian zeolitic tuff

الملخص: The reaction of aniline with hydrogen atom is investigated herein using the hybrid meta-DFT functional of BB1 K. Hydrogen atom is found to preferentially add at an ortho position. However, the fate of the o-(C6H5NH2)H adduct is found to be solely the deactivation of the initial addition channel. The rate constant for the abstraction channel (C6H5NH2 + H → C6H5NH + H2) is fitted by the expression 1.10 × 10−11 exp(−4,200/T) cm3 molecule−1 s−1. Our calculated rate constant for the abstraction channel agrees very well with the available experimental measurements. Satisfactory agreement is found between calculated and experimental measurements for the displacement channel (C6H5NH2 + H → C6H6 + NH2). Our detailed analysis for the corresponding displacements in toluene and phenol suggests that the three systems exhibit similar behavior with regard to the relative importance of abstraction and displacement channels.

الملخص: The effluent ponds from phosphoric acid and fertilizer industries are a worldwide problem. Wastewater in these ponds contains high concentration of acids and heavy metals that seriously contaminates the environment and underground water. On the other hand, it contains valuable components such as phosphoric acid, fluorine and flousilicic acid. In this work, wastewater samples from effluent pond of the Indo Jordan Chemicals (IJC) plant were collected. These samples were characterized for their pH, and chemical composition. The pH of pond water was found to be about 0.8 due to its high content of HF, H2SiF6 and H3PO4. Potentiometric titration, chloride and fluoride ion selective electrodes and other acid base titration methods were employed to determine the content of the above acids. AAS was also used to determine the content of heavy metals in this waste water. Potentiometric titration curves were produced to determine the optimum neutralization conditions for several synthetic mixtures made from the above acids, and for real effluent wastewater. XRD, XRF and SEM analyses were employed for analysis of the products of calcium hydroxide neutralizations. It was found that fluorine is present in effluent pond water in two forms: HF and H2SiF6. Precipitation experiments revealed that the reaction of H2SiF6 with Ca(OH)2 yielded only CaF2 with no CaSiF6. Furthermore, it was found that it is possible to separate sulfate in an initial precipitation stage. Additionally, it is possible to remove almost all fluoride in the form of CaF2 leaving at least 60% of H3PO4 in water. Amorphous silica could be removed by aging the solution after fluoride removal.

الملخص: Oil shale in Jordan and elsewhere faces many obstacles that hinder its utilisation. Recent developments of the utilization of Jordanian oil shale include the establishment of power generation companies that depend on the technology of atmospheric fluidized bed combustion systems (FBC). Sintering is believed to have been the main cause of many operational problems of FBC systems. This work investigates the sintering propensity of ash obtained from oil shale from Jordania’s largest oil shale deposit El-Lajjun, when combusted at different temperatures, as well as major mineral transformations as a function of temperature. The results obtained by the pressure drop sintering technique showed that the sintering temperature is a strong function of the combustion temperature. Two regions of sintering were found: a low temperature sintering region and a high sintering temperature region. The low sintering temperature region starts at around 700 °C where it is believed to be due to the sintering of limestone. On the other hand, the high sintering temperature region, which starts at 900 °C, is believed to be due to the sintering of the wollastonite formed. Scanning Electron Microscope (SEM) images and Brunauer–Emmett–Telle (BET) measurements confirm these findings

الملخص: The main object of this study was to study the effect of pyridine, 2-methyl pyridine, 3-methyl pyridine, 2,6-dimethyl pyridine, quinoline and tribenzylamine on the hydrolysis kinetics of benzoyl chloride in water-dioxane solutions. The investigation has been made by means of gas-liquid chromatography measurements. Almost equal rate constants have been determined for the hydrolysis reaction of benzoyl chloride in dioxane solutions. The catalytic effect of the studied range of tertiary amines on the hydrolysis reaction of benzoyl chloride was determined

الملخص: The main goal of this paper was to introduce an environmental fate and risk assessment methodology for comparing and establishing the general features of new and existing non-volatile organic chemicals (NVOCs) used in agricultural activities, based on simple and readily available properties. This methodology is a computer program called the multimedia agricultural fate and risk assessment model (MAFRAM). This model is a combination of the EQC-2V model, which describes the fate of NVOCs, with the ecological relative risk (EcoRR) approach, which assesses the ecotoxicological risk to agro-ecosystems. MAFRAM divides the agricultural environment into two main zones, which are the on- and off-farm zones. Each zone is subdivided into six compartments, including the air, water, soil, sediment, aboveground plants, and roots. The required input data are the chemical–physical properties of the pesticide, biota data, and environmental properties. The MAFRAM output includes the inter-compartmental transport and transfer rates, the primary loss mechanisms, chemical concentration, amount, residence time, and the rank of risk in each compartment. In addition, it can provide several secondary results. The MAFRAM application was illustrated using typical homogenous region properties and was run with an illustrative emission rate of 1 kg/h into air, using spinosad as a case study.

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الملخص: The purpose of the study is to investigate the optimum conditions for the precipitation of sodium hexafluorosilicate (Na2SiF6) from waste hexafluorosilicic acid, an effluent from the phosphoric acid industry. Sodium chloride and sodium hydroxide were used as reactants to produce Na2SiF6. The effect of various parameters on the precipitation was investigated and includes; the molar ratio of the reactants, contact time, the temperature and the effect of seeding.The optimum reaction conditions were found to be as follows; excess sodium chloride or sodium hydroxide to hexafluorosilicic acid of 25%, contact time 40 minutes and a reaction temperature of 40°C.The reaction of hexafluorosilicic acid with an aqueous solution of sodium chloride at optimum conditions gave a maximum yield of 94.26% Na2SiF6 while the reaction of hexafluorosilicic acid with the aqueous solution of sodium hydroxide at optimum conditions gave a maximum yield of 97.3% Na2SiF6. The X-Ray diffraction (XRD) analysis reveals that the only crystals present in the precipitate are Na2SiF6. Also, Scanning Electron Microscope (SEM) analysis shows that the different morphology of these crystals depend on the precipitation conditions

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