Statistical analyses of precious metal contents in waste incineration bottom ashes

Abstract

The recovery of precious metals from incinerator bottom ash (IBA) is a way of moving towards a circular economy. The paper presents a detailed analysis of the concentration of precious metals in IBA. The average values of precious metals in the samples analyzed are: Ag—6973 ppb, Au—313.90 ppb, Pd—41.26 ppb, Pt—13.81 ppb—all of these values being many times higher than the values of these elements in the Earth’s crust. The time series of the precious metals in the IBA were analyzed to assess the trend, seasonality, and outliers and to detect differences between the designated seasons of the year. Data analysis was performed following the CRISP-DM methodology using statistical and data mining methods. The analyzes confirmed a higher Ag concentration than in comparable European waste incinerator plants. The Au concentration was comparable to those reported in other incinerators, while the values were lower for Pt and Pd. The time series of precious metals shows no trend and seasonality, but numerous outliers. Due to the stationarity of precious metals, recovery can be expected to be constant, and the presence of numerous outliers can increase the potential return on investment.