Dear all,
I worked on adsorption of 2 nutrients and 1 toxic metal in biochar (mono and ternary-adsorption). It is for a possible stabilization of nutrient and pollutant in tropical soils. The results I found are very higher than those in litterature (for example about 1,200-2,800 mg/g for PO4 maximal adsorption capacity). Anybody can help me?
There is the method used :
To assess biochar capacity to adsorb the elements in environmental areas, both single-ion and ternary-ion adsorption experiments were conducted. Adsorption performances of the ions by biochar were assessed by means of both the Freundlich and Langmuir adsorption isotherm equations. Single-ion adsorption isotherms of ions were obtained by weighing 0.1 g of biochar from each test in plastic bottle. Then, 25 mL of ionic solution containing particular concentrations of the ions was introduced in the plastic bottle. After providing 24 h for the system to reach equilibrium, all samples were equilibrated for 24 h on an orbital shaker (SeaStar, Germany) at constant room temperature. At the end, the supernatant was filtered through a Whatman filter (0.45 mm) and then analyzed for ion concentrations.
Ternary-ion adsorption isotherms were determined by following the same procedure as the single-ion experiment using the same concentration ratio for the ions. For each ion, concentration levels of 0, 10, 40, 160, 330, 1,300, 10,000, and 25,000 mg/L were individually evaluated. The amount of ion adsorption by each biochar was calculated from the concentration reduction in solution.
And which are the adsorption capacities? 2800 mg/g phosphate?? This is too much. Check again.
I repeated the experiment three times with three replicates. I also determined adsorption capacity as function of time, pH et temperature: same level ranges !
I agree,depends up on the procedure u followed for preperation of adsorbent.
Analyse nature of adsorbent and then go ahead.
Dear Shafi,
Thank for your answer. My adsorbent is a biochar. All papers I saw indicate phosphate maximal adsorption capacity below 900 mg/kg. I determined PO4 level in initial and equilibrium solutions (Ci and Ce, resp.), and I applied the formula : q = (Ci - Ce)*V/m (were V: volume of the solution, and m: mass of biochar). The maximal adsorption capacities I determined are very high.
On the other hand, Ci max is 1,000 mg/L for all papers, whereas my study needed Ci max > 10,000 mg/L (or even 25,000 mg/L) !
I would suggest that you better quantity your biochar materially. Was it the same as other biochars to which you are comparing? I think that it is hard to get exactly the same biochar as another study unless you actually get the same material from the other group or purchase it from a manufacturer. I would recommend, if you are able, to take a close look the specific surface area, pore size distribution, FTIR spectra, TGA plot, and cationic exchange capacity of your biochar versus that of others. I think your result could be real. It might that you can explain the higher adsorption capacity based on more functional groups, more surface area, or higher mineral content in your biochar versus other papers.
Regarding what you say above concerning the 10,000 mg/L or 25,000 mg/L PO4, you might be measuring higher biochar adsorbed concentration just because you are using a large amount of adsorbate compared to others. I'm not certain when you say "maximum adsorption capacity" if you are talking about the actual amount you measured on the biochar or a predicted maximum capacity based on modeling the qmax term in the Langmuir isotherm.
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