Ferric chloride forced hydrolysis is shown to be a good method for increasing the iron content of... more Ferric chloride forced hydrolysis is shown to be a good method for increasing the iron content of activated carbons (ACs). Iron content increased linearly with hydrolysis time, and ACs with iron content as high as 9.4 wt.% at 24 h hydrolysis time could be prepared. The increase in iron content did not produce any modification in the textural parameters determined by nitrogen adsorption at 77 K. Iron-based nanoparticles, homogeneous in size and well-dispersed in the carbon matrix, were obtained. Nanoparticles forming iron (hydr)oxide agglomerates at the outer surface of the carbon grains at hydrolysis times higher than 6 h were also produced.
Arsenic removal from natural well water from the state of Chihuahua (Mexico) is investigated by a... more Arsenic removal from natural well water from the state of Chihuahua (Mexico) is investigated by adsorption using a commercial activated carbon (AC). The latter is used as such, or after oxidation by several chemicals in aqueous solution: nitric acid, hydrogen peroxide, and ammonium persulphate. Raw and oxidised activated carbons are fully characterised (elementary analysis, surface chemistry, pore texture parameters, pH ZC , and TEM observation). Adsorption of As is measured in the aforementioned water, containing ca. 300 ppb of arsenic: removal of As is poor with the raw AC, and only the most oxidised carbons exhibit higher performances. By contrast, iron-doped ACs are much more efficient for that purpose, though their As uptake strongly depends on their preparation conditions: a number of samples were synthesised by impregnation of raw and oxidised ACs with HCl aqueous solutions of either FeCl 3 or FeCl 2 at various concentrations and various pH. It is shown that iron(II) chloride is better for obtaining high iron contents in the resultant ACs (up to 8.34 wt.%), leading to high As uptake, close to 0.036 mg As/g C. In these conditions, 100% of the As initially present in the natural well water is removed, as soon as the Fe content of the adsorbent is higher than 2 wt.%. (V. Fierro). ferric arsenates, which are the most common arsenic precipitates, are unstable under some definite conditions and are therefore not suitable for direct disposal, otherwise As could be released in the environment . Ion exchange is the process by which chlorides or other anions bound at the surface of a resin are exchanged with arsenic-based anions from the solution. This process has the disadvantage of releasing harmful chemicals into the environment when the resin is regenerated . Finally, membrane processes are commonly employed, but this technology is expensive, mainly because of the high energy requirements .
Highly mesoporous activated carbons (ACs) with a mesopore fraction ranging from 42 to 73% were ob... more Highly mesoporous activated carbons (ACs) with a mesopore fraction ranging from 42 to 73% were obtained by activation of rice straw (RS) with ortho-phosphoric acid (PA). Due to such a high mesoporosity, these ACs can be successfully used for pollutant removal in aqueous phase. The ACs were prepared at activation temperatures (T) ranging from 350 to 500 • C, using PA to RS weight ratios (R) from 0 to 1.6 and activation times from 0 to 2 h. They were characterised by nitrogen adsorption at −196 • C, SEM-EDX, and methylene blue adsorption. RS is a very heterogeneous material with a variable content of mineral matter: using the product of activated carbon yield multiplied by surface area (C × S BET ) as the performance criterion, the best AC was produced at T = 450 • C and R ≥ 1. These conditions lead to S BET higher than 500 m 2 g −1 and a C × S BET around 270 m 2 g −1 . (V. Fierro). sodium hydroxide on the other hand [7]. In our previous paper [5], three pre-treatment protocols were tested: mechanical, chemical (by NaOH pulping), and a combination of both, followed by a further activation with KOH according to either one or two steps. Employing the combined mechanical-chemical pre-treatment method and a 2-steps KOH activation process, surface areas as high as 1917 m 2 g −1 could be obtained. However, the use of such complex activation protocol working at temperatures as high as 800 • C makes RS-based AC production rather expensive.
Ferric chloride forced hydrolysis is shown to be a good method for increasing the iron content of... more Ferric chloride forced hydrolysis is shown to be a good method for increasing the iron content of activated carbons (ACs). Iron content increased linearly with hydrolysis time, and ACs with iron content as high as 9.4 wt.% at 24 h hydrolysis time could be prepared. The increase in iron content did not produce any modification in the textural parameters determined by nitrogen adsorption at 77 K. Iron-based nanoparticles, homogeneous in size and well-dispersed in the carbon matrix, were obtained. Nanoparticles forming iron (hydr)oxide agglomerates at the outer surface of the carbon grains at hydrolysis times higher than 6 h were also produced.
Arsenic removal from natural well water from the state of Chihuahua (Mexico) is investigated by a... more Arsenic removal from natural well water from the state of Chihuahua (Mexico) is investigated by adsorption using a commercial activated carbon (AC). The latter is used as such, or after oxidation by several chemicals in aqueous solution: nitric acid, hydrogen peroxide, and ammonium persulphate. Raw and oxidised activated carbons are fully characterised (elementary analysis, surface chemistry, pore texture parameters, pH ZC , and TEM observation). Adsorption of As is measured in the aforementioned water, containing ca. 300 ppb of arsenic: removal of As is poor with the raw AC, and only the most oxidised carbons exhibit higher performances. By contrast, iron-doped ACs are much more efficient for that purpose, though their As uptake strongly depends on their preparation conditions: a number of samples were synthesised by impregnation of raw and oxidised ACs with HCl aqueous solutions of either FeCl 3 or FeCl 2 at various concentrations and various pH. It is shown that iron(II) chloride is better for obtaining high iron contents in the resultant ACs (up to 8.34 wt.%), leading to high As uptake, close to 0.036 mg As/g C. In these conditions, 100% of the As initially present in the natural well water is removed, as soon as the Fe content of the adsorbent is higher than 2 wt.%. (V. Fierro). ferric arsenates, which are the most common arsenic precipitates, are unstable under some definite conditions and are therefore not suitable for direct disposal, otherwise As could be released in the environment . Ion exchange is the process by which chlorides or other anions bound at the surface of a resin are exchanged with arsenic-based anions from the solution. This process has the disadvantage of releasing harmful chemicals into the environment when the resin is regenerated . Finally, membrane processes are commonly employed, but this technology is expensive, mainly because of the high energy requirements .
Highly mesoporous activated carbons (ACs) with a mesopore fraction ranging from 42 to 73% were ob... more Highly mesoporous activated carbons (ACs) with a mesopore fraction ranging from 42 to 73% were obtained by activation of rice straw (RS) with ortho-phosphoric acid (PA). Due to such a high mesoporosity, these ACs can be successfully used for pollutant removal in aqueous phase. The ACs were prepared at activation temperatures (T) ranging from 350 to 500 • C, using PA to RS weight ratios (R) from 0 to 1.6 and activation times from 0 to 2 h. They were characterised by nitrogen adsorption at −196 • C, SEM-EDX, and methylene blue adsorption. RS is a very heterogeneous material with a variable content of mineral matter: using the product of activated carbon yield multiplied by surface area (C × S BET ) as the performance criterion, the best AC was produced at T = 450 • C and R ≥ 1. These conditions lead to S BET higher than 500 m 2 g −1 and a C × S BET around 270 m 2 g −1 . (V. Fierro). sodium hydroxide on the other hand [7]. In our previous paper [5], three pre-treatment protocols were tested: mechanical, chemical (by NaOH pulping), and a combination of both, followed by a further activation with KOH according to either one or two steps. Employing the combined mechanical-chemical pre-treatment method and a 2-steps KOH activation process, surface areas as high as 1917 m 2 g −1 could be obtained. However, the use of such complex activation protocol working at temperatures as high as 800 • C makes RS-based AC production rather expensive.
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