Batch metal removal by peat. Kinetics and thermodynamics

Abstract

Abstract--Peat moss, a natural inexpensive material, is able to play an important rrle in treatment processes of metal-bearing industrial effluents since it adsorbs, complexes or exchanges various metal cations. This paper presents kinetics and thermodynamics of batch metal removal reactions by 50 g l-(dry wt) eutrophic or oligotrophic peat particles using Cu 2+, Cd :÷, Zn 2÷ and Ni 2÷ concentrations ranging from 0.01 to 100raM.Metal cation removal reactions are moderately rapid in l0 mM metal unbuffered solutions: the forward kinetic constant ranges between 0.005 and 0.17 M-Is-~, and equilibrium is reached within about 1 h. Under these conditions of pH (2.2-4.2) and concentrations, apparent binding equilibrium constants were found to range between 2 and 3150 M -~ depending upon the peat origin and the metal cation.In 0-6.5 pH-buffered metal cation solutions, the four cations binding reactions behaved differently demonstrating that metal binding equilibrium constant decrease in the order Ni 2+ > Cu 2+ > Cd 2+ = Zn 2÷ . When pH is higher than 6.7, more than 90% of a 10 mM metal cation solution is removed by 50 g 1 -t peat particles and metal binding capacities equal 200 mmol kg-~ dry wt, whatever the metal nature and the peat origin. Except for nickel cation which is very strongly bound to peat, all metal cations are completely released when pH is fixed below 1.5.

Sorption of Copper(II) from Aqueous Solution by Peat

“…Several biosorbents have been used as materials to adsorb copper from wastes including coconut coir husk (Low et al, 1995a,b), coir pith carbon (Namasivayam and Kadirvelu, 1997), agriculrural byproducts (Marshall et al, 1993) and chitosan (Findon et al, 1993;Ngah et al, 2002). Equilibrium studies on the use of peat to remove cadmium, copper, chromium, lead, mercury, nickel and zinc from a wide range of metal bearing wastewaters (Gosset et al, 1986;Viraraghavan and Dronamraju, 1993;Allen et al, 1992;Sharma and Forster, 1993;Ho et al, 1995;Ho and McKay, 2000;Ho et al, 2002).…”

Adsorção de zinco e cádmio em colunas de turfa

“…Na 5,10,20 . A eficiência do tratamento aplicado à turfa pode ser verificada no presente trabalho pelo aumento de 92% na capacidade de troca catiônica para a turfa tratada em relação à turfa in natura.…”

“…A turfa foi submetida a tratamento ácido de acordo com o procedimento indicado por Gosset, Trancart e Thévenot 10 , com a finalidade de disponibilizar os seus sítios de adsorção, além de eliminar os cátions metálicos que poderiam estar fixados à sua estrutura.…”

Retention Time Effect on Metal Removal by Peat Columns

“…Equilibration rates of metals in solution with peat moss are very rapid (Crist et al 1996;Gosset et al 1986;Gardea-Torresdey et al 1996). In experimental systems, copper equilibrium is reached within 30 minutes of contact with peat moss.…”

“…This is also the case with other metals that can be removed. There are differences in the binding strength of divalent metals (Gosset et al 1986;Brown et al;Crist et al 1996). The order can vary slightly, based on the exact conditions of contact, but the usual order of affinity of removal is Pb>Cu=Ni>Cd=Zn.…”