# Prediction of Total Petroleum Hydrocarbons and Heavy Metals in Acid Tars Using Machine Learning
## 2 Materials and Methods  
Sampling, preparation, and coding of the acid tar samples from the lagoon. The sampling procedure was done according to BS EN 14899:2005. Characterization of waste. Sampling of waste materials. Framework for the preparation and application of a sampling plan. This method is applicable for samples of untreated acid tar, neutralized tar, or stabilized tar in force (Order no. 95/2005).  
Experimental layout. A lagoon area of 10.55 ha was used for this study. Sampling was carried out in acid tar sampling points from 5 cm, respectively, 30 cm depth, and following the STEREO 70 coordinates of the sampling points.  
The characterization of the acid tar and the finite treated products was made by the determination of the following key indicators: pH, THP content, metals, chlorides, dissolved organic carbon (DOC), sulfites, total of dissolved solids (TDS), and total of organic carbon (TOC) [26]. According to Order 95 from 2005, to be deposited and accepted in deposits, the waste must have certain chemical properties [27]. This is why a specific analysis was conducted for the studied and treated acid tars. Also, the validation of the treatment process necessitated the performing of the leachate test.  
Treatability testing program. The treatability studies specific to the studied lagoon and studies performed at a laboratory scale offered the necessary data for feasibility treatment recipe determination.  
The working program had the following steps [26]:  
* Sample collection;
* Initial samples characterization;
* Sample homogenization;
* Performing the chemical tests;
* Performing the treatability tests;
* Performing the test by mixing the reactants with the contaminated material and the formulation preparation for the next tests;
* Blending the design optimization;
* Selection of the mixture design verifying phase;
* Design and final test preparation;
* Data analysis, evaluation, and validation of recipes proposed and applied to the studied acid tars.  
Laboratory analysis  
Determining the TPH content. The determination of the TPH content was made using the gas-chromatographic method (GC-FID), according to the SR EN ISO 16703:2011 testing method.  
Heavy metals and As concentrations. Metal concentrations were established according to the SR EN ISO 15586:2004 Analysis Method: Determination of Trace Elements by Graphite Furnace Atomic Absorption Spectrometry using a Graphite Furnace Atomic Absorption Spectrometer.  
Our proprietary acid tar stabilization technology consists of the following [25; 26]:  
* Mixing the acid tar with powdered hydrated lime by bringing the pH to alkaline values (pH = 9-10) and passing the heavy metals into insoluble combinations, following the neutralization reaction with additives to stabilize the pH.
* The solidification and stabilization of acid tar by mixing with hydraulic binders and emulsifiers, which produces the encapsulation of contaminants in granular and uniform particles, blocking the possibility of their spreading in the environment.  
The final validation of the recipes proposed and applied to the acid tar in the studied lagoon is being done by comparing the leachate/eluate indicators with the maximum allowed values for the leachate obtained from the acid tar, according to Order 95/2005 [27].