The partition coefficient of the solute i was then calculated according to Eq. 1. LLC experiments were carried out on a counter current chromatography column, model HPCCC-Mini Centrifuge from Dynamic Extractions , with a column volume of 18.2 mL. Two isocratic Gilson 306 pumps , equipped with an 806 Manometric Module , were used for delivering the mobile and stationary phases. The elution profiles were monitored with a DAD 171 diode array detector at a wavelength of 220 nm. The CCC experiments were performed at room temperature. All LLC separations were carried out as pulse injections in DSC mode, where the lower phase is used as mobile phase. At the beginning of each experiment, the column was filled with stationary phase. Afterwards, the rotational speed was set to 1900 rpm and the mobile phase was pumped through the column at 1 mL min−1 until no more stationary phase eluted from the column. The samples were dissolved in the corresponding mobile phase , filtered and then injected via a 1 mL sample loop with a manual injection valve, with the mobile phase continuously pumped at 1 mL min−1. All CCC runs were manually fractionated after injection in fraction intervals of 1 min. The collected fractions were analyzed by HPLC-DAD. Based on the analysis of the fractions, a reconstructed offline LLC-chromatogram was generated for each separation run. GC-TCD analysis was performed using a Nexis GC 2030 coupled with a thermal conductivity detector from Shimadzu . A Restek Rxi-624Sil MS capillary column was used, with helium as carrier gas at a linear velocity flow of 40 cm s−1. The temperature of the injection port was set to 250 °C, at a split-ratio of 50 during injection. After an isothermal step of 1 min at 35 °C, a linear temperature gradient of 31 °C min−1 to 190 °C was applied. The TCD temperature was set at 260 °C. The biphasic solvent systems were prepared in 20 mL vials by mixing the corresponding portions of the solvents at ambient temperature and pressure.

The mixture was then vigorously shaken and equilibrated at 25 °C for 2 h. Then, 100 μL of upper and lower phases were separately diluted with 900 μL THF and their compositions were analyzed by GC-TCD, using six-point calibration curves established for each of the analyzed solvents. In this work, a computer-aided approach for selecting biphasic solvent system candidates for preparative LLC isolation of CBD from hemp extracts,cannabis grow supplies with simultaneous removal of contaminating pesticides that might be present in the starting material is proposed. First, a list of biphasic solvent systems from a predefined pool of solvents was created. After that, a fully predictive thermodynamic model was used to screen for potential systems . The objective of the screening was to identify biphasic solvent systems in which the partition coefficient of the target component CBD is within a predefined range. Three of the most promising solvent systems were next evaluated in terms of their ability to separate the target compound CBD from a list of pesticides as impurities. In this work, pesticides whose limits in cannabis products are regulated by the state of Oregon were considered. Consequently, a list of critical pesticides was determined for each solvent system based on separation factors αCBD/PEST values predicted by COSMO-RS and validated by shake-flask experiments . For the proof-of-concept, a hemp extract spiked with seven pesticides was subjected to LLC separations with each of the three selected solvent systems . To demonstrate the applicability and validity of the approach shown above for the selection of solvent systems for the preparative LLC separation of CBD from potentially contaminated hemp extracts, seven representative pesticides from the red, orange and yellow zones were selected. These were added to a decarboxylated hemp extract that was further subjected to LLC separations with each of the three solvent systems. The separations were performed on a lab-scale CCC column, in DSC mode at 1 mL min−1 and 1900 rpm. The feed mixture was injected in the column in a concentration of 5 mg mL−1 hemp extract spiked with 50 ppm of each pesticide. In all separations, a stationary phase retention of 0.6 was achieved.

Even though the pesticide concentrations for spiking might exceed those existing in real hemp batches, they were selected taking into consideration the higher LODs and LOQs of the UV detector of the HPLC-DAD system used to perform the off-line analyses of the collected fractions. The reconstructed off-line chromatograms presenting the individual fraction concentrations vs. elution time are depicted in Fig. 5. The peak shapes in Fig. 5 for CBD and each pesticide were obtained by fitting the experimental data points into Gaussian equations with Origin2020 software. The on-line chromatograms recorded with the DAD detector of the CCC set-up is presented in Fig. S1 . As expected from PCBD EXP values from Table 2, the yellow-zoned and green-zoned pesticides as well as trifloxystrobin were completely removed during the LLC separation with solvent system I . Nevertheless, ethoprophos and kresoxim methyl, cinerin I and pyrethrin II were partly co-eluting with CBD peak. In the case of solvent system II, the pesticides from yellow and orange zones were eliminated, with the exception of the highly critical pesticides cinerin II and pyrethrin II that strongly overlapped with the CBD peak; trifloxystrobin only partly co-eluted. Since none of the selected pesticides were in the red zone in solvent system III, the separation with this system showed the best outcomes, most of the pesticides being totally eliminated, while ethoprophos and cinerin II slightly overlapped with the CBD peak . Lignite is still an important source of energy in many countries of the world. Poland is the second lignite producer in European Union after Germany , and fourth in the world . Presently about 30 % of Poland’s energy is generated from brown coal . Lignite mining in Poland covers approximately 16 000 ha while the area of land degraded as a result of open mining activity is over 67 000 ha . Opencast mining is the most common technique used for mining of coal and other minerals when they occur close to the surface . Surface coal mining causes a lot of disturbances in the ecology of the natural environment. Sometimes, far-reaching geological and ecological changes may even lead to international conflicts and legal disputes . Opencast mining leads to significant geomechanical transformations and degradation of the natural structure of the soil profile and the layers of the natural cover of humus, one of the basic components of soil that determines its fertility. Before the lignite can be excavated by the open-mining method the top layer over the lignite deposit – so called overburden – has to be removed together with all the vegetation and the soil.

Surface mining drastically alters soil properties, destabilizes soil organic carbon and depletes SOC pools. Carbon is initially lost from mined soils in the same manner that organic C is lost from tilled soils due to the disintegration of soil aggregates that leads to organic matter being decomposed and carbon is ultimately respired . After the coal deposit mined with the opencast method is exhausted, a dead excavation remains, which is filled with material from the outlay as the excavation progresses. The surface of such terrain is leveled.The humus content in such a layer is trace, it does not have a biologically active surface layer consisting of mineral and organic particles of varying degrees of disintegration. When natural components of the environment have lost the capability to autoregenerate in a timely manner, their rehabilitation is only possible through anthropogenic correction. Natural processes of soil formation are slow and can take decades or centuries to form new soil. To speed up soil formation processes and to achieve a normal soil productivity level different procedures of land reclamation ale implemented, leading to construction of a new soil. The characteristics of this new soil or minesoil depend on the kinds and sequences of reclamation procedures employed . There are many possible options for the productive uses of reclaimed mine lands. This does not necessarily imply restoring precisely the characteristics of the premine soil and landscape but rather involves the establishment of geological and hydrologically stable landscapes capable of supporting a natural mosaic of ecosystems. The implementation of any one of the land use possibilities is conditioned by technical, economic, social, and environmental aspects . There are three main directions for the restoration of the post-mining areas. These are agricultural use when arable lands, cannabis grow facility permanent grassland or orchards are set up, afforestation of reclaimed areas that have a production or protective function and a special direction based on recreational, ecological or aesthetic and protective management. Agricultural reclamation is not the most common. The direction of reclamation in each country is selected for each case separately. In Great Britain for example, as well as in Germany and Hungary, the agricultural approach of reclamation is preferred while in the United States and Turkey the forestry approach dominates. In Poland many disturbed areas are used for recreational purposes . Among lignite mines in Poland, agricultural reclamation is used on a larger scale by only two mines – “Adam´ ow” and “Konin” .

Globally, agricultural reclamation is carried out mostly by cultivating a small number of non-food plants, which are then used industrially. In our opinion, this is not the optimal solution. From an industrially degraded area, where the process of creating a humus layer has just begun, biomass is extracted, resulting in low yields of succeeding crops, and the reclamation process is ineffective and extended over time. Devastated soil has a diverse geomechanical composition and deficiencies of some essential nutrients are common, which makes it unsuitable for the production of food or fodder plants. We propose here the use of fiber hemp cultivation as a pioneering plant, when all the produced biomass is not removed from the field but is reintroduced into the soil in order to restore the missing humus layer as quickly as possible. Hemp is an herbaceous plant that can grow from about 1–6 m tall, depending on factors such as cultivar and environmental and agronomic conditions. It can produce high amount of biomass. Some authors reported very high yields of hemp reaching more than 22 tons per hectare , however more typical values are lower and other authors report yields of fiber hemp on the level of 7− 15 tons per hectare . Fibre hemp is a traditional industrial crop in many regions of the world. For many centuries hemp has been cultivated mostly as a source of strong stem fibre and seed oil . Recently this species gains a lot of attention for its alternative use directions, these include using hemp for biomass and biofuel production. Hemp is a rapidly growing plant that tolerates high planting density and the total biomass of hemp per hectare is similar to other energy crops, including giant miscanthus, poplar or willow. However, hemp may provide a key advantage; its bast fibers contain high amount of cellulose and low amount of hemicelluloses and lignin comparing to other biomass crops. The stem biomass in hemp consists of high cellulose fiber; thus, the ratio of digestible sugars to lignin is higher in hemp than in other similar-yielding biofuel crops . In addition to a high amount of biomass, the plant has a well-developed taproot system, growing into the soil to a depth of about 2 m or more. Hemp’s short growing cycle, decreased need for pesticides, and low plant maintenance makes it an ideal candidate for phytoremediation utilization . Cannabis sativa is also plant potentially usable for the detoxification of contaminated soils due to its resistance to soil contamination, its ability to accumulate heavy metals and possibility of cultivation in different climatic conditions . All these unique characteristics of hemp and the awareness that vegetation plays a major role in improving the properties of mine soils, where increased biomass production, root residues and exudates, and the greater activity of microbes following revegetation have positive effects on the accumulation of soil organic matter has encourage us to test the study the usefulness of fibre hemp as a species for experimental reclamation of the 7.5 ha area degraded by previous lignite mining operations.