Cynthia A. Coles

Kaolinite properties, structure and influence of metal retention on pH

Abstract The differences between kaolinite and smectite structures are notable, mainly as a result of the degree of weathering in the different compounds. Nevertheless, the kaolinite structure possesses great advantages in many processes due to its high chemical stability and low expansion coefficient. As a consequence of adsorption, the kaolinite structure and the soil solution pH will change. To analyze the adsorption behaviour of kaolinite, Pb, Zn and Cd were studied at three different concentrations (1, 2 and 3 mmol/l) and over different periods of exposure (0.1, 1, 2, 4, 8, 12 and 24 h). The kaolinite retained up to 10.0 μmol/g of Pb, 8.40 μmol/g of Zn and 6.00 μmol/g of Cd when it was mixed with the 3 mmol/l concentration of heavy metals. In each case, the adsorption eventually reduced the solution pH from 4.6 to 3.7. The changes in pH over time indicated both the release and retention of hydrogen ions by the mineral, probably involving the hydroxyl edge sites and exposed hydroxyl planes. The size of the atomic radii are 1.81, 1.71 and 1.53 A for Pb, Cd and Zn, respectively, compared to the 0.79 A for H. This difference, along with the differences in hydrated radii, will affect the structure of the clay causing stress in the molecule. Changes in the mechanical and chemical properties of the clay are discussed as the interactions of the heavy metal cations with the kaolinite could affect the structure of the kaolinite and influence properties such as swelling capacity, compaction capability and the double-layer behaviour. The kaolinite in this study contained some illite which may have increased the pH 7 cation exchange capacity to 17.8 mEq/100 g. Using the adsorption data, the reactions at the clay water interphase and the probable effects on the physical properties and structure of kaolinite are discussed.

Aspects of kaolinite characterization and retention of Pb and Cd

This study illustrates the complimentary nature of selected techniques for characterizing kaolinite. For the particular type of kaolinte studied, scanning electron micrographs revealed the presence of crystallites and mostly larger than clay-sized particles. These findings were in agreement with the low cation exchange capacity, low specific surface area, low zero point of charge and high purity that were determined for the kaolinite. Batch equilibrium tests were conducted on kaolinite suspensions that had been adjusted to pH 4 and pH 6. These suspensions were spiked with varying concentrations of Pb (as PbCl2) and Cd (as CdCl2). At equilibrium, the metal uptake was greater for the pH 6 suspensions than for the pH 4 suspensions, the metal uptake was generally greater when greater concentrations of metal had been used to spike the suspensions, and there was a reduction in suspension pH that accompanied the metal uptake. A comparison of the equilibrium curves of both metal retention and suspension pH, as a function of the initial metal concentration, combined with an analysis of metal speciation, provided evidence for the adsorption of both divalent (Pb2+ and Cd2+) and monovalent (PbCl+ and CdCl+) species by the kaolinite. Cation exchange was a primary retention mechanism and the order of selectivity for the pH 4 and pH 6 suspensions of kaolinite appeared to be Pb2+>H+>Cd2+. At higher pH and higher metal concentrations, there was an increase in Cd uptake relative to Pb uptake. This may have been a result of less competition between H+ ions and metal ions for adsorption sites, and because CdCl+ forms at a lower salt concentration than PbCl+, and so a greater proportion of monovalent Cd was adsorbed.

Influence of Bulking Agents, Fertilizers and Bacteria on the Removal of Diesel from a Newfoundland Soil

Laboratory experiments in culture flasks, containing diesel-contaminated Newfoundland soil samples, were undertaken to compare the influence of fertilizers, microorganisms and bulking agents on bioremediation. In Phase I experiments only one fertilizer (cow manure or poultry manure), one bulking agent (sand or hay), or one inoculum (cold-tolerant indigenous bacteria or exogenous commercial bacteria) was added to a soil sample. In Phase II experiments, Design-Expert® Version 6 design of experiment software determined the combinations of fertilizers, bulking agents and inocula to be mixed with the soil samples to study the interactions among the amendments. The maximum diesel removal at 90 days occurred in the sample with sand (Phase I) and in the sample with cow manure, an inoculum of cold-tolerant indigenous bacteria, and sand (Phase II). Diesel removal at 45 days for the same two samples was 85.4% (Phase I) and 91.9% (Phase II), suggesting the cow manure and/or cold-tolerant bacteria inoclum accelerated the process. The poultry manure, commercial bacteria and hay were less effective than their counterparts. The commercial bacteria were more sensitive to diesel concentration than the indigenous cold-tolerant bacteria. The addition of sand, cow manure, and poultry manure improved diesel removal.

Leaching of Chromium, Copper, and Arsenic from CCA-Treated Utility Poles

Concentrations of Cu, Cr, and As in soils surrounding 26 Douglas Fir Chromated Copper Arsenate (CCA) treated utility poles and in rainwater runoff from a new CCA treated utility pole segment (log) suspended outside in a cylinder were studied. The age of the utility poles, distances from the poles, rainfall amounts, and characteristics of soil samples including cation exchange capacity (CEC), pH, and total organic carbon (TOC) were considered. Heavier rainfall, damp conditions, and more weathered poles contributed to the greatest leaching of Cu, Cr, and As. The maximum measured soil concentrations of Cu, Cr, and As were 37.5, 65.5, and 38.9 mmol/kg and maximum Cu, Cr, and As concentrations in rainwater run-off were 14, 77.7 and 55.8 μmol/L. Metal concentrations decreased with distance from the poles and, except at one utility pole location, Cu was the most leached of the three elements. The As appeared to have greater mobility in the soil than the Cr. Along the transmission line nearest the coast and from which the greatest amount of samples was collected, soil CEC and TOC values were the highest and the CEC and TOC were directly and strongly correlated.

Peat Characterization and Uptake of Nickel (II) and Cobalt (II) in a Saprist Peat Column

In this study, fibrist and saprist sphagnum peat soils taken from a bog in Torbay, Newfoundland (Canada) were characterized. The saprist and fibrist peat soils had wet bulk densities of 0.65 and 0.60 g/cm3, respectively, and cation-exchange capacities of 70 and 45 meq/100 g, respectively. The pH of both peat soils was 4.2 and the soils were amorphous for the most part; however, the fibrist peat was more porous than the saprist peat. Results of Fourier transform infrared spectroscopy and 13carbon nuclear magnetic resonance suggested the presence of carboxylic acid, alcoholic hydroxyl, phenolic hydroxyl, amine and amide functional groups in both peats. The less reported amine and amide groups may have been observed because non-destructive characterization techniques were employed. The saprist peat was studied as an Ni2+ and Co2+ adsorbent in a vertical downflow fixed-bed column and at the end of each column experiment, metal ions in the upper layer of the peat were desorbed with HCl. The metal sorption capacity of the saprist peat increased with decreasing flow rate and overall the sorption capacity of Ni2+ was two times greater than the sorption capacity of Co2+. Ni2+ may have been retained by a combination of ion exchange and complexation, while Co2+ may have been retained only by complexation.

Modeling the Sorption of Ni2+ and Co2+ on Saprist Peat Using the Response Surface Methodology

A detailed study of the sorption of Ni2+ and Co2+ from simulated wastewater on saprist peat is presented. The significantly decomposed peat possessed a strong sorptive capacity that was maintained over a wide range of pH. With a metal concentration range of 50 to 200 mg/L, pH range of 3 to 10, peat dose of 2 to 40 g/L, and contact time of 12 to 24 h, batch experiments were conducted based on a four-factor Box-Behnken response surface design. The percentage removals of Ni2+ and Co2+ were analyzed using analysis of variance. Second order response surface models were developed with the significant factors and their interactions to predict the percentage sorption of Ni2+ and Co2+ independently. The prediction equations were verified with additional data not used in developing the equations. The study showed that the saprist peat could be a potential industrial metal adsorbent and the percentage of uptake of Ni2+ and Co2+ could be accurately predicted using the second order response surface models developed. Ni2+ uptake was greater for the two metals and reached a maximum value at just below a neutral pH and Co2+ uptake continued to increase from pH > 5, with higher uptake percentage at pH 10.