# Testing of Natural Sorbents for the Assessment of Heavy Metal Ions' Adsorption
## 2 Materials and Methods  
### Materials  
The cost of sorbents is one of the necessary requirements for sorbents to ensure the possibility of wide application. In this regard, it is rational to use primarily inexpensive materials as sorbents [26]. Based on these economic criteria, this paper researches the generally accepted natural sorbents for the assessment of heavy metal ions' adsorption, such as peat, diatomite, vermiculite and their mixtures in different proportions and physical shapes. The following materials have been employed in the study (Table 1). The first material was neutralized high-moor fractionated peat (fraction 0-10), with a peat moisture content from 50% to 60%, pH in the range of 5.5-6.0 and ash content of less than 5%. The main inorganic peat compounds were nitrogen (up to 1.5%), phosphorus, potassium and calcium (in total) up to 0.6%. The content of humic substances was 7.4-7.9%. Peat was mixed with diatomite in the mass ratio of 2/1. Diatomite is a soft, lightweight, thin-pored massive material consisting of the mass of the smallest (0.01-0.04 mm) opal shells of bacillariophytes. Their density is usually nearly 0.5-0.7 g/cm\({}^{3}\), and its porosity reaches 70-75% [27]. \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline
**Sorbent Name** & **Ratio** & **Moisture** & **Ash Content** & **Apparent** & **Specific Surface Area** & **Temperature** \\  & **(\%)** & **pH** & **(\%)** & **(\%)** & **Density (kg/m\({}^{3}\))** & **of Grains (m\({}^{2}\)/kg)** & **(K)** \\ \hline
1. Granular peat-diatomite & 50\% & 6.5-7.5 & 15 & Less than 5 & 215 & 1.94 & 295 \\
2. Non-granular peat-diatomite & 50\% & 6.5-7.5 & 25 & Less than 5 & 272 & 0.05 & 295 \\
3. Diatomite & 100\% & 8.5-9.5 & 2 & Less than 1 & 465 & 0.15 & 295 \\
4. Large-fraction vermiculite & 100\% & 5.5-6.0 & 8 & Less than 1 & 134 & 3.24 & 295 \\
5. Medium-fraction vermiculite & 100\% & 5.5-6.0 & 8 & Less than 1 & 145 & 2.17 & 295 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristics of the natural sorbents discussed in the study. The apparent density of the peat and diatomic mixture was 272 kg/m\({}^{3}\). Parts of this mixture were formed in granules in the screw pelletizer with further drying in the drum-type drier at a temperature of 80 \({}^{\circ}\)C. The heat treatment of the pellets was completed when the humidity reached 25%. The apparent density of the absorbent grains was 242 kg/m\({}^{3}\), taking into account that the specific surface area of the grains was 1.94 m\({}^{2}\)/kg. The second material was medium-fraction vermiculite (fraction 1-4 mm) with an apparent density of 145 kg/m\({}^{3}\), as well as large-fraction vermiculite (fraction 5-10 mm) with an apparent density of 134 kg/m\({}^{3}\) and a specific surface area of 3.24 m\({}^{2}\)/kg. Vermiculite is a mineral from the hydromicas group which turns into a flowing lamal material during heat treatment [28]. Vermiculite improves the soil structure, absorbs the excess moisture, loosens the soil and increases the soil breathability. The third material was model toxicants, which are the individual solutions of salts of heavy metals and arsenic related to them, including CuSO\({}_{4}\)\({}^{5}\)H\({}_{2}\)O, Pb(NO\({}_{3}\))\({}_{2}\), Cd(NO\({}_{3}\))\({}_{2}\)*\({}^{4}\)H\({}_{2}\)O, Cr\({}_{2}\)(SO\({}_{4}\))\({}_{3}\)*\({}^{6}\)H\({}_{2}\)O, K\({}_{2}\)Cr\({}_{2}\)O\({}_{7}\) and NaAsO\({}_{2}\). To prepare the solution, a sample of salt was dissolved in a measuring container. Solutions with lower concentrations were prepared from the resulting initial solution by dilution. As a result, solutions of salts with the following titers (content) of heavy metals were procured: T(Cr+3) = 1.0 mg/L, T(Cr+6) = 0.5 mg/L, T(Pb+2) = 1400 mg/L, T(Cu+2) = 635 mg/L, T(Cd2+) = 10000 mg/L and T(As3+) = 5.0 mg/L.