###### Abstract  
This research examines the possibility of the washing process as a supplementary operation after extensive extended physical separation sequences for processed incinerator bottom ash (pr.IBA), which is the mineral fraction resulting from conventional separation operation of municipal solid waste (MSW) incinerator bottom ash (IBA) in Germany. Citric acid is employed as the only primary treatment agent in several variations of parameter combinations. It includes the type of solvent, washing duration, acid concentration, liquid-to-solid ratio, and introduction of external agitation (stirring and heating). The analysis results revealed that the concentration of copper, zinc, and manganese in the mineral phase of pr.IBA can be reduced by the citric acid washing process. The most significant change is observed in the zinc content, where a reduction of up to 50% is successfully achieved. In contrast, the silicon concentration is relatively unaffected during citric acid washing, but a concentration decrease is detected for calcium. The aluminum and iron contents in the studied fraction of pr.IBA are also soluble in citric acid solution, although the rates are expected to be exceptionally slow. In this instance, stirring and heating over a prolonged washing duration are necessary before a decrease in their concentration can eventually occur. citric acid; washing treatment; MSW incinerator; bottom ash; recycling Article  
[PERSON]RESS], [PERSON], [PERSON], [PERSON], R.  
concrete production [5, 6]. Despite already being processed using state-of-the-art separation techniques employing screening, magnetic, and eddy current separation sequences, yielding physically and chemically stable aggregates comparable to the quality of primary materials remains a critical challenge. In this case, in addition to the commonly used physical separation methods, which are usually conducted after natural weathering (aging), wet treatment or washing is a common alternative for increasing the quality of IBA [7], especially in reducing the content of the heavy metal and their leachability. There are relatively numerous published reports related to the washing process of IBA. The first is the water washing process, one of the most widespread techniques that claims to successfully reduce some contaminants and heavy metals [8, 9, 10, 11]. The performance of this washing process can also be improved by introducing acid into the system. Some researchers who applied the concept were [PERSON] and [PERSON] [12], using varied nitric acid concentrations. Based on their observations, the highest acid concentration achieved the maximum removal efficiency for most heavy metals, amplifying the findings of a previous report published by [PERSON] and [PERSON] [13]. Another alternative approach was taken by [PERSON] et al. [14] by using organic acids, given their advantages in terms of the environment and safety during utilization. According to their experiments, citric acid solutions can also effectively remove heavy metals from raw IBA. Similar positive results were reported by [PERSON] et al. [15] and [PERSON] et al. [16], despite revealing the main drawback of applying the concept is the massive amount of wastewater that must be treated later. It is worth mentioning that the required wastewater treatment contaminated with citric acid is associated with a more straightforward neutralization process [17, 18], biodegradable residue, and lower cost than treating wastewater contaminated with strong acid. Nonetheless, regardless of the solvent used during the process and the technological alternative to treat wastewater, the washing process is still troublesome to a certain extent because the new waste will be generated after the wet treatment of the IBA, which is originally part of another waste management system.