Development of green technology for extraction of nickel from spent catalyst and its optimization using response surface methodology

Strict environmental legislation and increasing energy demand are the foretokens to edify the need of an eco-friendly sustainable method of metal extraction from spent catalysts. The present study practices an eco-friendly chelation technology for extraction of nickel from spent catalyst. Experiments were carried out with chelating agents diethylenetriaminepentaacetic acid (DTPA) and nitrilotriacetic acid (NTA), in addition to our previous published data on (S, S)-ethylenediamine disuccinic acid [(S, S)-EDDS] and ethylenediaminetetraacetic acid (EDTA), by adopting the "one variable at a time" (OVAT) approach. However, OVAT does not take into account the interaction effect of process variables and cannot be regarded as an accomplished approach for multivariate analysis. Therefore, an attempt has been made to explore the applicability of response surface methodology (RSM) in order to minimize experimental efforts and provide elaborated quality of information to overcome the limitations of OVAT. A Box-Behnken design (BBD) was coupled with RSM to optimize the process parameters using statistical analysis. The quantitative evaluation of the data shows that the molar ratio of chelating agent to Ni, solid to liquid ratio, and time, exert a significant influence on Ni extraction. A high value of regression coefficient (R-2 >0.97) substantiated a well fitted quadratic empirical model. The present optimization study may prove utilitarian for hydroprocessing industries intending to extract metals from spent catalyst which may reduce processing costs also.