Jaakko Rämö

The importance of ligand speciation in environmental research: a case study

The speciations of EDTA and DTPA in process, waste and river waters are modelled and simulated, specifically to the mode of occurrence in the pulp and paper mill effluents and subsequently in receiving waters. Due to relatively short residence times in bleaching process and waste water treatment and slow exchange kinetics, it is expected that the thermodynamic equilibrium is not necessarily reached. Therefore, the initial speciation plays a key role. As such, the simulations have been extended to the process waters of the pulp and paper industry taking into account estimated average conditions. The results reveal that the main species are; Mn and Ca complexes of EDTA and DTPA in pulp mill process waters; Fe(III) and Mn complexes of EDTA and DTPA in waste waters; Fe(III) and Zn complexes of EDTA and DTPA in receiving waters. It is also shown how the increasing concentration of complexing agents effects the speciation. Alkaline earth metal chelation plays a significant role in the speciation of EDTA and DTPA when there is a noticeable molar excess of complexing agents compared with transition metals.

Effect of biological wastewater treatment on the molecular weight distribution of soluble organic compounds and on the reduction of BOD, COD and P in pulp and paper mill effluent.

Pulp and paper mill wastewater was characterizated, before (influent) and after (effluent) biological wastewater treatment based on an activated sludge process, by microfiltration (8, 3, 0.45 and 0.22microm) and ultrafiltration (100, 50, 30 and 3kDa) of the wastewater samples into different size fractions. Various parameters were measured on each fraction: molecular weight distribution (MWD) using high performance size exclusion chromatography (HPSEC), total organic carbon (TOC), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total phosphorus (Tot-P), phosphate phosphorus (PO(4)-P), electrical conductivity, pH, turbidity, charge quantity and zeta potential. The MWD, TOC and COD(Cr) results indicated that the majority of the material present in both the influent and effluent was in the medium molecular weight (MW) range (i.e. MW<10kDa) with three main MW sub-fractions. There were no significant differences in the range of the MWD between the influent and effluent samples. The magnitude of the MWD in the effluent was about one half that in the influent, the greatest reduction being in the 6kDa fraction. The 3kDa fractions of both the influent and effluent showed a considerable increase in BOD(7), probably due to the removal of compounds harmful to bacteria in 3kDa ultrafiltration. Influent turbidity decreased considerably in microfiltration (8-0.22microm). As the turbidity was removed by 0.22microm filtration, the anionic charge quantity started to decrease. Particles in the influent and effluent contained 19-29% and 14-20% of the total phosphorus, respectively. The major phosphorus fraction was in the form of soluble phosphate.

Size fractionation of wood extractives, lignin and trace elements in pulp and paper mill wastewater before and after biological treatment.

Integrated kraft pulp and paper mill wastewater was characterized before (influent) and after (effluent) the activated sludge process by microfiltration (8, 3, 0.45 and 0.22 microm) and ultrafiltration (100, 50, 30 and 3 kDa) into different size fractions. Wood extractives, lignin, suspended solids and certain trace elements were determined in each fraction. Forty four percent of the resin and fatty acids in the influent (12.8 mg/L) occurred in particles (>0.45 microm), 20% as colloids (0.45 microm-3 kDa) and 36% in the <3 kDa fraction. The corresponding values for sterols (1.5 mg/L) were 5, 46 and 49%. In the effluent, resin and fatty acids (1.45 mg/L) and sterols (0.26 mg/L) were mainly present in the <3 kDa fraction, as well as a small proportion in particles. beta-sitosterol was present in particles in the effluent (88+/-50 microg/L). Lignin in the influent was mainly in the colloidal and <3 kDa fractions, whereas in the effluent it was mainly in the <3 kDa fraction. Thus the decrease of lignin in the biological treatment was concentrated on the colloidal fraction. In the influent, Mn, Zn and Si were mainly present in the <3 kDa fraction, whereas a significant proportion of Fe and Al were found also in the particle and colloidal fractions. In the effluent, Fe and Al were mainly present in the colloidal fraction; in contrast, Mn, Zn and Si were mainly in the <3 kDa fraction. The results indicated that the release of certain compounds and elements into the environment could be significantly decreased or even prevented simply by employing microfiltration as a final treatment step or by enhancing particle removal in the secondary clarifier.

Degradation of EDTA by hydrogen peroxide in alkaline conditions

Abstract The decomposition of EDTA was studied in a pilot-plant flow-through system simulating an alkaline (pH 10–11) hydrogen peroxide bleaching environment. Results obtained by gas chromatography were compared with calculated concentrations and the percentage of the residual was calculated on this basis. The amount of hydrogen peroxide decomposition was evaluated and the chelate distribution calculated. The results revealed that, under the conditions investigated, the residual averaged 94%, with lowest value 79%. An average of 26% hydrogen peroxide was decomposed during the experiments.

Chemical sequential extraction of heavy metals and sulphur in bottom ash and in fly ash from a pulp and paper mill complex.

A five-stage sequential extraction procedure was used to determine the distribution of 11 metals (Cd, Cr, Cu, Mo, Pb, Zn, As, Co, V, Ni, Ba), and sulphur (S) in bottom ash and in fly ash from a fluidized bed co-combustion (i.e. wood and peat) boiler of Stora Enso Oyj Oulu Mill at Oulu, Northern Finland, into the following fractions: (1) water-soluble fraction (H2O); (2) exchangeable fraction (CH3COOH); (3) easily reduced fraction (NH2OH—HCl); (4) oxidizable fraction (H2O2 + CH3COONH 4); and (5) residual fraction (HF + HNO3 + HCl). Although metals were extractable in all fractions, the highest concentrations of most of the metals occurred in the residual fraction. From the environmental point of view, this fraction is the non-mobile fraction and is potentially the least harmful. The Ca concentrations of 29.3 g kg—1 (dry weight) in bottom ash and of 68.5 g kg— 1 (dry weight) in fly ash were correspondingly approximately 18 and 43 times higher than the average value of 1.6 g kg— 1 (dry weight) in arable land in Central Finland. The ashes were strongly alkaline pH (∼ 12) and had a liming effects of 9.3% (bottom ash) and 13% (fly ash) expressed as Ca equivalents (dry weight). The elevated Ca concentrations indicate that the ashes are potential agents for soil remediation and for improving soil fertility. The pH and liming effect values indicate that the ashes also have a pH buffering capacity. From the environmental point of view, it is notable that the heavy metal concentrations in both types of ash were lower than the Finnish criteria for ash utilization.

Comparison of hydrolysis products of AlCl3 ·6H2O in different concentrations by electrospray ionization time of flight mass spectrometer (ESI TOF MS)

Hydrolysis of 0.100, 0.010, and 0.001 mol L−1 aqueous solutions of AlCl3·6H2O, each at two pH values ranging from 3.27 to 7.00, was compared by electrospray ionization time-of-flight mass spectrometry. The differences between 4 h and 14 day aged solutions were also studied. Various charges and compositions for species of the same size were observed. At lower pH values, dimeric and trimeric aluminium oxo-hydroxo-complexes were the major molecular species. With higher pH levels, precipitation and formation of took place. Multiple charged signals assigned to polynuclear complexes (Al10–Al15) were found at a narrow pH area range before precipitation occurred. The diversity of different species increased strongly as a function of concentration. The pH of the solution dominated the profile even more than the concentration. All the main species were formed in 4 h.

Acid mine drainage treatment using by-products from quicklime manufacturing as neutralization chemicals.

The aim of this research was to investigate whether by-products from quicklime manufacturing could be used instead of commercial quicklime (CaO) or hydrated lime (Ca(OH)2), which are traditionally used as neutralization chemicals in acid mine drainage treatment. Four by-products were studied and the results were compared with quicklime and hydrated lime. The studied by-products were partly burnt lime stored outdoors, partly burnt lime stored in a silo, kiln dust and a mixture of partly burnt lime stored outdoors and dolomite. Present application options for these by-products are limited and they are largely considered waste. Chemical precipitation experiments were performed with the jar test. All the studied by-products removed over 99% of Al, As, Cd, Co, Cu, Fe, Mn, Ni, Zn and approximately 60% of sulphate from acid mine drainage. However, the neutralization capacity of the by-products and thus the amount of by-product needed as well as the amount of sludge produced varied. The results indicated that two out of the four studied by-products could be used as an alternative to quicklime or hydrated lime for acid mine drainage treatment.

Sulphate removal over barium-modified blast-furnace-slag geopolymer

Blast-furnace slag and metakaolin were geopolymerised, modified with barium or treated with a combination of these methods in order to obtain an efficient SO4(2-) sorbent for mine water treatment. Of prepared materials, barium-modified blast-furnace slag geopolymer (Ba-BFS-GP) exhibited the highest SO4(2-) maximum sorption capacity (up to 119mgg(-1)) and it compared also favourably to materials reported in the literature. Therefore, Ba-BFS-GP was selected for further studies and the factors affecting to the sorption efficiency were assessed. Several isotherms were applied to describe the experimental results of Ba-BFS-GP and the Sips model showed the best fit. Kinetic studies showed that the sorption process follows the pseudo-second-order kinetics. In the dynamic removal experiments with columns, total SO4(2-) removal was observed initially when treating mine effluent. The novel modification method of geopolymer material proved to be technically suitable in achieving extremely low concentrations of SO4(2-) (<2mgL(-1)) in mine effluents.

Identification of hydrolysis products of AlCl 3 ·6H 2 O in the presence of sulfate by electrospray ionization time-of-flight mass spectrometry and computational methods

ElectroSpray Ionization-Mass Spectrometry (ESI-MS) and computational methods (DFT, MP2, and COSMO) were used to investigate the hydrolysis products of aluminium chloride as a function of sulfate concentration at pH 3.7. With the aid of computational chemistry, structural information was deduced from the chemical compositions observed with ESI-MS. Many novel types of hydrolysis products were noted, revealing that our present understanding of aluminium speciation is too simple. The role of counterions was found to be critical: the speciation of aluminium changed markedly as a function of sulfate concentration. Ab initio calculations were used to reveal the energetically most favoured structures of aluminium sulfate anions and cations selected from the ESI-MS results. Several interesting observations were made. Most importantly, the bonding behaviour of the sulfate group changed as the number of aqua ligands increased. The accompanying structural rearrangement of the clusters revealed the highly active role of sulfate as a ligand. The gas phase calculations were expanded to the aquatic environment using a conductor-like screening model. As expected, the bonding behaviour of the sulfate group in the minimum energy structures was distinctly different in the aquatic environment compared to the gas phase. Together, these methods open a new window for research in the solution chemistry of aluminium species.

Performance of a commercial industrial-scale UF-based process for treatment of oily wastewaters.

An evaluation was made of the performance of a commercial industrial-scale ultrafiltration (UF)-based process for treatment of highly concentrated oily wastewaters. Wastewater samples were gathered from two plants treating industrial wastewaters in 2008, and in 2011 (only from one of the plants), from three points of a UF-based treatment train. The wastewater samples were analyzed by measuring the BOD7, COD, TOC and total surface charge (TSC). The inorganic content and zeta potentials of the samples were analyzed and GC-FID/MS analyses were performed. The removal performances of BOD7, COD, TOC and TSC in 2008 and 2011 for both plants were very high. Initial concentrations of contaminants in 2011 were lower than in 2008, therefore the COD and TSC reductions were also lower in 2011 than three years before. Regardless of the high performance of UF-based processes in both plants, at times the residual concentrations were considerable. This could be explained by the high initial concentrations and also by the presence of the dissolved compounds that were characterized. Linear correlation was observed between COD and TOC, and between COD and TSC. The correlation between COD and TSC could be utilized for process control purposes.