A research into sorption properties of peat briquettes used to remove ions of cadmium, lead and copper from wastewaters

Abstract

Introduction. At present, the following areas are the subject of intensive research: methods for removing such toxic metals as cadmium, lead, copper, etc. from wastewaters, namely, using new composite sorbents for this purpose; improvement of ion exchange treatment and, for example, sedimentation of sulphides or oxalates; wood ash sorption; biosorption onto plants. It is a future-oriented trend to use peat as a sorbent in a wastewater treatment technology. Extensive peat deposits in the Republic of Belarus can contribute to production of cheap, environmentally friendly sorbents made of modified peat briquettes. The mission of this work is to study the sorption properties of peat briquettes used to remove cadmium, lead and copper ions from wastewater. Materials and methods. Physicochemical, technological, mathematical methods are employed. Results. The co-authors studied the kinetics of cadmium Cd+2, lead Pb+2, and copper Cu+2 ions sorption onto peat briquettes. They identified that the bigger the grain of peat briquettes, the less efficient the sorption. The sorption process is intensive: it takes cadmium Cd+2, lead Pb+2, and copper Cu+2 ions five minutes to get extracted from the solution; extraction efficiency reaches 91.11; 96.96 and 88.39 %, respectively. 20 minutes is enough to reach degree of equilibrium F = 0.98 for cadmium Cd+2 and lead Pb+2 and F = 0.96 for copper Cu+2. F is equal to 0.99 for all ions in 40 minutes. The multiplicity of extraction, or the ratio of initial concentration to equilibrium concentration reaches 114 for cadmium ions Cd+2, 162 for lead ions Pb+2, and 93 for copper ions Cu+2. In case of saturation, sorption capacity reaches the following values: Сd+2 — 0,0778 mmol/g (8.75 mg/g), Pb+2 — 0.8205 mmol/g (170.00 mg/g), Cu+2 — 2.707 mmol/g (172 mg/g). The co-authors used equations of diffusion and chemical kinetics to establish that the sorption process proceeds in the diffusion mode, and the stage of chemical interaction of metal ions with functional groups of peat contributes to the overall velocity of the process. Conclusions. Peat briquettes represent an effective sorbent used to remove cadmium Cd+2, lead Pb+2, and copper Cu+2 ions from wastewater. The sorption process is almost over in 20 minutes.