I did an experiment on Copper and Lead precipitation at different pH levels beginning from 4 to 7. In one recent published paper, I found the precipitation of Lead at pH 7 is somewhat 84% whereas in my experiment it was 88%. It is to be mentioned that the conditions and the usage of apparatus were totally different in my experiment from the published work.
Besides, at pH 4 and 5, I did not find any precipitation for Copper. But some studies done on Acid Mine Drainage aspect found that Copper precipitates mostly withing 3-4.5 pH range.
Why these results differ like this? I thank everyone in advance for reading this and sharing some opinions or answers from experience.
The precipitation of metals as a function of pH also depends on other chemical species in the solution, since chemical speciation will affect metal solubility, and on the presence of solid phases, which can potentially act as adsorbents.
It is also important to note that the solubilities near the transition from soluble to insoluble are difficult to accurately measure, since the transition is rather sharp, so you should be be surprised that your results will differ by a few percent or even more compared to published results.
You may consider performing geochemical modelling (e.g. using freely available Visual MINTEQ) to help understand the pH dependency and the mechanisms.
+++ for Visual MINTEQ!
And it also depends on the concentration of metal in the solution.
MEDUSA software - which is free like Visual MINTEQ - can also be helpful. You can construct diagrams to see the species (with its fractions) in solutions and compounds that precipitates in any solution system. It is a user-friendly software.
Link for MEDUSA: http://www.kth.se/en/che/medusa/
About the difference between the removal efficiency in your work and the other work it is acceptable because the removal efficiency depends on the initial concentration of substrate in the solution
Precipitation depends on temperature and ionic strength in solution. competitive coumpound can also affect efficiency of precipitation.
Dear Sirajus: While the equilibrium constants for each solide phase you may produce in your experiment are absolute for a given temperature, the variation in the composition of the tested solutions, as well as the pH and Eh values in each experiment can all produce different conditions for metals precipitation. So, heavy metals precipitation does not have to be necessarily in the same way.
Laking basic information about your experiments, my advice is to: 1) Try to find out in your experimental conditions what species of each element could be expected to be present; 2) define each mass would be tested for each element, and, 3) try then a chemical speciation model, as some colleagues indicated, and compare with your especific esperimental conditions. Ok? Go ahead and good luck!
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