Recovery of detox tea wastes: Usage as a lignocellulosic adsorbent in Cr6+ adsorption

As a result of increasing population, developing technology, and growing industrial activity year by year, the release of heavy metals to the environment is continually increasing. Therefore, the treatment of heavy metals is of great importance for the protection of the environment. Lignocellulosic agricultural waste can be used as a versatile, adsorbent material for heavy metals. This article aims to evaluate experimental results on the behavior of various tea wastes for removal of Cr6+ under internal and external factors affecting adsorption properties. The effects of different parameters such as initial pH (2-7), adsorbent quantity (0.5-5.0 g/100 mL), stirring speed (50 - 300 rpm), contact time (5 -120 min) were assessed. The suitability of Cr6+ adsorption to different isotherms and kinetics was also investigated. According to the CalcPlot3D, the order of the parameters that profoundly affect adsorption was pH > adsorbent dose > time > temperature > stirring speed. An assessment of Delta H degrees, Delta S degrees, Delta G degrees obtained during the adsorption process showed that waste black tea (WBT), waste green tea (WGT), waste rooibos tea (WRT) were applicable, spontaneous, endothermic for Cr6+. The maximum removal efficiency for Cr6+ was achieved under optimum conditions as 88 %, 83 %, and 73 %. According to the data obtained, the equilibrium adsorption was observed to fit Langmuir. The maximum adsorption capacity for WBT, WGT, WRT was 9.14, 8.56, and 5.12 mg/g, respectively. The adsorption of Cr6+ on WBT, WGT, WRT was defined by pseudo-second-order. All results showed that raw WBT, WGT, WRT was environmentally friendly, low cost, an easily available adsorbent in removing Cr6+ from aqueous solution.