The ameliorative effects of low-grade palygorskite on acidic soil

Mineral composition and alkaline properties of palygorskite (Pal), and its ameliorative effects on chemical properties of acid soil were investigated. Dolomite was the main form of alkali in Pal and the acid neutralisation capacity of Pal was 215 cmol kg–1. Incubation experiments indicated that Pal incorporation increased soil pH, cation exchange capacity, base saturation and exchangeable K+, Na+, Ca2+ and Mg2+ contents, and decreased the levels of exchangeable H+, Al3+ and acidity, over a 1-year period. The ameliorative mechanisms were the dissolution of major alkaline matter in Pal (i.e. dolomite), and the exchange between released Ca2+ and Mg2+ with H+ in acidic soil. Hence, Pal can be used as a moderate acidic soil amendment.

Characterisation of Oyster Shell for Neutralisation of Bio-leached Effluent

Characterisation studies of Oyster Shell (Mercenera mercenera) collected from coastal towns of Ghana and its neutralising effect on bio-leached effluent has been studied using XRF, XRD, Zeta Meter, BET and SEM/EDX. The study confirmed that OS contains high calcium equivalent to about 54% CaO. The OS consists mainly of aragonite (96.1%) and calcite (2.6%) which are carbonates hence OS can be used to neutralise any acid solution. OS is very hard to mill as it has high Bond work index of 48.54 kWh/t. The Zeta Potential analysis indicates that OS will not be stable below pH of 3 and above pH of 10. Therefore OS powder dissolved and raised the pH of bio-leached effluent from pH 1.85 to 6.0 in 30 minutes. The arsenic removal increased with increasing OS concentration. The morphological study revealed that the surfaces of the reacting particles were coated with precipitates like FeAsO4 at pH of 4.5. Consequently, surface area of reacting powder increased from 4.15 m2/g to 75.46 m2/g. In a similar manner, the D50 decreased from 16.69 µm to 7.77 µm for the reacting particles at pH 4.5. Particle size distribution at pH 7.0 showed that the D50 of the OS material increased to 9.23 µm which can be due to coating of precipitates like CaSO4 on the reacting particles during acid neutralisation. Mobile arsenic extracted from the precipitate averaged 6.42 mg/L as against the EPA maximum allowable concentration of 5.0 mg/L indicating that the precipitate formed is fairly stable. Keywords: Effluent, Neutralisation, Oyster Shells, Characterisation, Work Index

Monitoring the Acid Neutralisation Capacity and Options for Leaching Iron from Waste Mud from the Production of Al2O3

Red and brown mud is created in the processing of bauxite into Al2O3. The chemical composition of red and brown mud depends upon the method of processing bauxite on a mud landfill, and the time and availability of mud leaching by rain. Samples of red mud from landfill in Žiarska Kotlina had pH values of 9.46 ± 0.11 and brown mud had 10.2 ± 0.15. We studied the development of changes in pH and concentrations of Fe (spectrometrically with AAS) in eluates during the leaching of red and brown mud samples. Results show that there is no release of Fe during brown mud elution. When using 0.025 and 0.05 M H2SO4 for elution, the pH decreased slightly from 10.2 ± 0.15 to 2.4 ± 0.05. Elution of 0.1 M H2SO4 shows that pH decreased to a value of 2.2 ± 0.05 by the 40th fraction and then it fell to a value of 1.77 ± 0.04 in the 100th fraction. The greatest amount of iron was released in the 8th and 55th fraction at a pH of 2 – 4 which could be observed by the change in colour of eluates. The progress of the release of iron was similar for both kinds of mud. Then we determined the neutralisation capacities of various fractions of mud in H2SO4, NaOH and H2O leachates by titration. It was discovered that the reaction of the alkaline proportions of red mud with the agent is greatest with fine granularity but for red mud, it does not change depending upon the size of the grain. The release of acid proportions depended upon time not upon texture. When leaching with water, the leached alkaline compounds from brown mud are mainly from the finest particles, and in the case of red mud, it was the opposite, from the largest particle fraction.

The response of a small stream in the Lesni potok forested catchment, central Czech Republic, to a short-term in-stream acidification

Lesni Potok stream drains a forested headwater catchment in the central Czech Republic. It was artificially acidified with hydrochloric acid (HC1) for four hours to assess the role of stream substrate in acid-neutralisation and recovery. The pH was lowered from 4.7 to 3.2. Desorption of Ca and Mg and desorption or solution of Al dominated acid-neutralisation; Al mobilisation was more important later. The stream substrate released 4,542 meq Ca, 1,184 meq Mg, and 2,329 meq Al over a 45 m long and 1 m wide stream segment; smaller amounts of Be, Cd, Fe, and Mn were released. Adsorption of SO42- and desorption of F‾ occurred during the acidification phase of the experiment. The exchange reactions were rapidly reversible for Ca, Mg and SO42-; but not symmetric as the substrate resorbed 1083, 790 and 0 meq Ca, Mg, and Al, respectively, in a 4-hour recovery period. Desorption of SO42-; occurred during the resorption of Ca and Mg. These exchange and dissolution reactions delay acidification, diminish the pH depression and retard recovery from episodic acidification. The behaviour of the stream substrate-water interaction resembles that for soil–soil water interactions. A mathematical dynamic mass-balance based model, MASS (Modelling Acidification of Stream pediments), was developed which simulates the adsorption and desorption of base cations during the experiment and was successfully calibrated to the experimental data. Keywords: Al, Ca, Mg, base cations, acid-neutralisation, stream acidification, recovery, stream sediment, experiment, modelling, adsorption, desorption, adsorption, Czech Republic, Lesni Potok