Waste recovery into activated carbon for water purification from heavy metals

The main objective of this research was the recovery of natural carbon-containing wastes into environmentally friendly secondary products, and their re-use as selective adsorbents for heavy metals removal from wastewater streams. The natural carbon containing wastes were: Sunflower husks, D-grade coal, AKKhZ sludge and Spent petroleum product waste. To achieve this purpose, the research was focused on three different types of studies: 1. Study the thermolysis process of the single carbon-containing wastes components and their blends aimed at: (i) determination of the reference onset of the thermal stages, assigning the reference structural fragments of the parent Sunflower husks, D-grade coal, AKKhZ sludge and Spent petroleum product waste; and (ii) evaluation of the synergetic effects observed during their co-thermolysis. 2. Development of a recovery concept to the waste recycling via co-activation of the co-mingled carbon-containing waste materials, in order to obtain a porous activated carbon. 3. Optimization of the experimental conditions for the adsorption of heavy metals from contaminated waste waters. In order to gain some insight into the reactions which may occur between the components of the co-mingled wastes during the activation process, in the first part of the work the pyrolysis behavior of the single components and their blends were investigated by thermogravimetric analysis. On this stage, the data obtained suggested a new approach to the problem of assessing the selectivity of the co-processing concept. Based on the direct monitoring of the reference structural fragments during co-thermolysis, the synergetic effects were evaluated for the co-mingled systems. The data obtained were used in the second part of the work, for the development of the co-activation concept to the co-mingled solid and liquid recovery into secondary solid porous products. The development of the design parameters for the activated carbons syntheses was done considering the re-polymerization, re-association and the polycondensation reactions between the reference structural fragments of the components in the ternary composite systems «Spent Petroleum Product Waste – Biomass – D-grade D» and «AKKhZ sludge – Biomass – D-grade coal». The factors influencing the char formation and the properties of the resulting activated carbons were evaluated at laboratory scale. The co-activation approach developed to the solid and liquid co-mingled waste recycling, was implemented at pilot scale. Novel powder and granular activated carbons have been obtained with surface area of 400-1050 m2/g, total pore volume of 0.32-0.47 m3/g and yield of 21-27%.A comprehensive adsorption study using the novel activated carbons, was performed in the third part of the work. The influence of various textural and surface characteristics of carbon materials (porosity, surface area, oxygen functional groups) and the conditions of the adsorption process (initial solution acidity, contact time, components ratio) were investigated in batch mode for single- and multi-component model solutions containing Fe (II), Co (II), Cu (II), Cr (III), Ni (II), Mn (II). Under optimized conditions, a total chromium uptake of 1.09 mmol/g was achieved using as adsorbent the novel activated carbon from co-mingled wastes. The uptake is slightly higher than the one obtained for the commercial GAC Norit 1240 Plus (A– 10128) activated carbon oxidised by HNO3. Moreover, in the course of this work, it became clear, that the usage of the activated carbon from co-mingled waste for the 3d transitional metals adsorption offered an attractive approach to simultaneous metal removal from multi-component solutions. The total metal removal combined the process of metal hydroxide precipitation (up to 50–55 % by total removal) with the metal cation adsorption on negatively charged carbon surface (up to 15–20 % by total removal) in a single operation unit. Finally, the mechanism of the 3d transition metals adsorption on the activated carbon from co-mingled waste was considered. Within this context, the natural organic waste recovery into porous solid environmentally friendly products offered a technological alternative to their disposal.