# Testing of Natural Sorbents for the Assessment of Heavy Metal Ions' Adsorption
## 3 The Results of the Experimental Studies and Discussion  
The results of testing the efficiency of the sorbents in relation to the heavy metal ions' adsorption are shown in Figure 1. The information in Figure 1 allowed for the evaluation of the efficiency of the studied sorbents in relation to the heavy metal ions' adsorption, which was shown during 70 h of the experiment. The maximum and close to the maximum possible heavy metal ion extraction from the solutions by sorbents of peat-diatomite and vermiculite of various fractions (medium and large) were noted. The granular sorbent peat-diatomite showed the greatest efficiency with respect to the ion binding of Pb\({}^{2+}\) and Cu\({}^{2+}\). In this case, the degree and quantity of extraction of these ions from aqueous solutes of salts were 100.0 and 98.0%. The granular sorbent peat-diatomite was less effective in relation to Cr\({}^{6+}\) ions (in the composition of Cr\({}_{2}\)O\({}^{7-}\) ions), As\({}^{3+}\) ions (AsO\({}^{2-}\)) and Cd\({}^{2+}\) ions. The degree of extraction of the listed ions by this sorbent was in a range from 60% to 80%. A fairly lower sorption efficiency of the granular sorbent peat-diatomite occurred with respect to the Cr\({}^{3+}\) ions. The non-granular sorbent peat-diatomite demonstrated nearly the same sorption efficiency as the granular sorbent peat-diatomite for the Pb\({}^{2+}\), Cu\({}^{2+}\) and As\({}^{3+}\) ions. This sorbent exhibited approximately half the capacity in relation to the chromium ions in a oxidation state +3, +6. For this sorbent, an anomalous decrease in the sorption capacity was observed in relation to the cadmium ions. The decrease occurred to a value which was comparable to the determination error of the quantitative content of the metal ions in the solution. The high efficiency of adsorption in relation to the heavy metal ions in the experiments were noted for large- and medium-fraction vermiculite. Regardless of the fractional composition, vermiculite almost completely bound the ions of Cd\({}^{2+}\), Cu\({}^{2+}\) and Pb\({}^{2+}\). At the same time, there was a five-fold difference in the sorption of As\({}^{3+}\) ions. Large-fraction vermiculite sorbed almost all of the arsenic in the solution (medium-fraction vermiculite = only 18.5%). The probable reason for this discrepancy may be the use in the study of vermiculite from different manufacturers. They use various technological processing for natural source raw materials. Meanwhile, vermiculite of both fractions practically did not show the sorption properties in relation to the Cr\({}^{6+}\) ions. The relevant experimental value of the adsorption was close to the value of the determination error. A relatively lower efficiency in the binding of heavy metal ions in the research was identified for diatomite. This material, when used as a sorbent, adsorbed 88.9% of Tb\({}^{2+}\) ions and 64.0% of Cu\({}^{2+}\) ions from the solution. These were the best results for this sorbent. Diatomite virtually did not bind cadmium. However, diatomite was 2.5 times higher than the medium-fraction vermiculite in terms of As\({}^{3+}\) ion adsorption. Figure 2 shows a general diagram for the studied sorbents and heavy metal salt solutions. Figure 2 demonstrates the total value of the adsorption of heavy metal ions. The granular sorbent peat-diatomite had the highest total efficiency in the sorption of the studied heavy metal ions. This was established based on the results of the sorbents' testing. Large-fraction vermiculite was almost as good as the granular sorbent peat-diatomite in terms of the indicator under consideration. The lowest efficiency was shown by the sorbent consisting of diatomite, which did not contain peat additives. Medium-fraction vermiculite and non-granular sorbent peat-diatomite took the intermediate position in terms of sorption efficiency. The difference in the sorption efficiency of the studied sorbents was linked to their chemical compositions and the structure of the adsorbing surface.