Cobalt Ion Adsorption by Carbon Nanostructured Materials of Sludge-Lignin Thermochemical Activation

One of the current problems of modern industry is the accumulation of waste. А methodology for selective purification of wastewater using waste products from the cellulose-paper industry, specifically lignin sludge, has been proposed to address the issue of waste accumulation. Pyrolysis is an effective method for converting lignin sludge into adsorbents. Activation of the pyrolysis products with alkaline reagents under laboratory conditions has allowed for the production of activated carbons. These obtained carbons are expected to selectively extract various ions from the wastewater. The study focused on the adsorption capacity of nanoscale carbon materials thermally activated with lignin sludge. A solution of cobalt chloride hexahydrate was used as a model wastewater solution. Co ions tend to form stable complex compounds with ethylenediaminetetraacetic acid anions and organic acids present in liquid waste. The cobalt complexes formed are stable over a wide range of pH and cannot be removed by precipitation methods or sorption without prior treatment with oxidants. The study proposed a solution to the problem of difficult cobalt extraction due to its tendency to form complexes by creating optimal conditions for the formation of an ammonia complex with subsequent extraction using an organic sorbent. The influence of pyrolysis conditions such as temperature (T), time (τ), and activator dosage (D) on response functions such as monolayer capacity, heat of adsorption, maximum adsorption capacity, and characteristic adsorption energy were investigated. These response functions provide insights into the porous structure of the activated carbon. A design of experiments method, specifically a rotatable central composite plan, was applied. Response surface plots were constructed based on experimental data for visualization. The analysis led to the development of practical recommendations for conducting the pyrolysis process to obtain a commercial product - activated carbons from lignin sludge.