Obtaining a Low Cost Adsorbent from a Biodegradable Polymer for the Removal of Low Molecular Organic Compounds from Solutions of Technological Origin

The work solves the problem of obtaining adsorbents from cheap and available feedstock able for the removal of low-molecular-weight toxic organic substances from aqueous solutions. It is proposed to obtain an adsorbent from the wastes of such biodegradable poly­mer as polylactic acid (PLA), for example, from used packaging. The polymer was heated up to the melting point, cooled and ground. The thermally treated PLA sample contained end carboxyl and hydroxyl groups, which were identified with Fourier-IR spectroscopy, and the ion-exchange activity of the polymer was found. These groups provide a surface charge density of 0.02−0.12 C m-2 in the pH range of 4−10, ξ-potential reaches 30 mV in an alkaline media. Adsorption of such cationic dye as methylene blue (MB) was studied under static and dynamic conditions. The Temkin and Freundlich models were applied to the adsorption isotherms, an increase in the adsorption capacity of the polymer was found with an increase in pH from 4 to 10, while the surface became more energetically heterogeneous. The capacity of PLA is 16−30 mg g-1 in the absence of a supporting electrolyte, and 10−28 mg g-1, when adsorption occurs from a two-component solution containing also NaCl. According to the results of the study of MB adsorption, and the data of electronic spectroscopy for suspension of the polymer, it was established that the dye removal from the solution occurs mainly due to electrostatic attraction to the negatively charged PLA surface. The adsorbent was proposed to be employed for the remo­val of the residual colour of wastewater after its treatment, for example, with reverse osmosis or nanofiltration.