I am performing adsorption experiments to remove lead ions on an bio-based adsorbent. I am optimising the parameters such as initial ion concentration,pH etc using Response surface methodology. I would like to know on what basis should I select the initial concentration range? I am targeting for lead contamination in industrial wastewater (India), and therefore want to prepare synthetic lead nitrate solution accordingly.
Hi,
The adsorption efficiency of your adsorbent is largely affected by the composition of the water matrix. Because the latge organic substances (humic and fulvic acids, for instance) will not be present in your synthetic water matrix, your efficiency will be lower in real water solutions, as compared to synthetic solution prepared in deionized water. Probably the optimal settings can therefore be different in between both water matrices.
In this sense, conducting experiments in synthetic water matrix in order to optimize the system will not give you so much of information. In order to get valuable results It would be much better to collect real water samples, analyze the lead concentration, and than try to optimize the process parameters, using your RSM approach.
Niels
Dear Uddipta Nath ,
I agree with Niels, I think you are going to start your project. my suggestion will be first optimize the pH then time of adsorption, adsorbent amount, you can also check the temperature effect and then concentration that will give you good informations. finally try the industrial sample.
The initial concentration is normally selected arbitrarily but remember this should be within your comfortable detection limits
Hi Uddipta, I agree with Niels and Rashid that we need to understand the composition of the industrial wastewater first when designing our experiment. From the composition we can use speciation software such as PHREEQC (https://www.ndsu.edu/webphreeq/) or Visual Minteq (https://vminteq.lwr.kth.se/) to understand the ionic species present, possibility of precipitation and so on. Once we know the main species of the target metal (which depends on pH) we can select an anionic or cationic adsorbent. It should be noted that adsorption is considered the right process if we wish to polish the wastewater (i.e. metal conentration is a few ppm). As Niels mentioned the presence of humic substances, for example, can effect the adsorption efficiency (http://jopr.mpob.gov.my/adsorption-of-npk-fertiliser-and-humic-acid-on-palm). What you could do is to study the adsorption starting with a simple single element solution to understand the kinetics, diffusion behaviour, sorption mechanism (physisorption, electrostatic or chemical) and type (single layer, multilayer). Use the pH of the real wastewater. Subsequently you may add another substance to the synthetic solution to study competition for sorption sites, precipitation phenomena and so on. In a third experiment you can add chelators that are present in the industrial ww to understand its effect. In order to select the suitable metal concentration you ideally need to know the sorption capacity of your adsorbent. If you don't then you can go through the literature (review papers) reporting sorption capacity for Pb by a variety of adsorbents. Once you got an idea of the sorption capacity (say 10 mg/g) we need to look at the amount of adsorbent we want to add to a certain volume. Again we can conduct a literature review to identify the most commonly used set-up. I use 0.5 g of adsorbent in 100 mL of solution. If we use this for the sake of argument we can now predict the concentration of Pb in solution required to completely remove it:
q = (c1-c2) x V / m
q is the sorption capacity [mg/g], c1 the initial Pb concentration [mg/L], c2 the final Pb concentration at equilibrium [mg/L], V is the volume of the solution [L] and m the mass of the adsorbent [g].
Plugging our values in and arranging the equation for c1 we get:
c1 = q x m / V = 10 mg/g x 0.5 g / 0.1 L = 50 mg / L
From here you can select concentrations that are below and above 50 mg/L.
On a slightly different but related note I would recommend to concentrate more on regeneration of the adsorbent and new applications of spent adsorbents instead of adsorption studies. There is not much value and potential for new discovery in this saturated field of adsorption. Just my two cents... Good luck anyway.
