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Gold is one of the precious metals with multiple uses, whose deposits are much smaller than the global production needs. Therefore, extracting maximum gold quantities from industrial diluted solutions is a must. Am-L-GA is a new material, obtained by an Amberlite XAD7-type commercial resin, functionalized through saturation with L-glutamic acid, whose adsorption capacity has been proved to be higher than those of other materials utilized for gold adsorption. In this context, this article presents the results of a factorial design experiment for optimizing the gold recovery from residual solutions resulting from the electronics industry using Am-L-GA. Firstly, the material was characterized using atomic force microscopy (AFM), to emphasize the material’s characteristics, essential for the adsorption quality. Then, the study showed that among the parameters taken into account in the analysis (pH, temperature, initial gold concentration, and contact time), the initial gold concentration in the solution plays a determinant role in the removal process and the contact time has a slightly positive effect, whereas the pH and temperature do not influence the adsorption capacity. The maximum adsorption capacity of 29.27 mg/L was obtained by optimizing the adsorption process, with the control factors having the following values: contact time ~106 min, initial Au(III) concentration of ~164 mg/L, pH = 4, and temperature of 25 °C. It is highlighted that the factorial design method is an excellent instrument to determine the effects of different factors influencing the adsorption process. The method can be applied for any adsorption process if it is necessary to reduce the number of experiments, to diminish the resources or time consumption, or for expanding the investigation domain above the experimental limits.

Statistical thinking and statistical methods play an important role in planning, conducting, analyzing and interpreting data from experiments. When several variables influence a certain characteristic of a product, the best strategy is then to design an experiment so that valid, reliable and sound conclusions can be drawn effectively, efficiently and economically. The present paper investigates the efficiency of chromium ions removal onto Amberlite XAD7 using the solvent impregnated resin (SIRs) method. The Amberlite XAD7 resin was impregnated with di-(2-ethylhexyl)-phosphoric acid (DEHPA) and ethylic alcohol as solvent by dynamic column impregnation method. The results showed that the maximum efficiency of chromium ions removal was reached after 60 min. At this moment, the efficiency of chromium ions removal was of ~90%. In this paper the design of experiments was used to study the performance of a chemical process. The process transforms the inputs into an output that has two observable responses (absorbability and efficiency). By analyzing the results of the second-order model, the process has been optimized.

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