Oktay Bayat

Characterisation of Turkish fly ashes

Abstract The mineralogical, morphological, physical and chemical properties of seven different fly ashes from eastern, central and western lignite and bituminous coal fields in Turkey are compared in this study. The mineral matter in the fly ashes, determined by means of X-ray diffraction, is dominated mainly by anhydrite, lime, quartz and hematite + ferrite spinel. The three low-calcium ashes—Soma, Seyitomer and Catalagzi—have the typical, relatively simple, crystalline phases Q, M, H and FS. The high-calcium fly ashes—Yenikoy and Afsin-Elbistan—have the most complex assemblage of crystalline phases. The much higher calcium concentrations in these samples result in the formation of lime (CaO), melilite [(Ca,Na)2(Mg,Al,Fe)(Si,Al)2O7] and merwiinite (possible phase) [Ca3Mg(SiO4)2]. The presence of anhydrite in all samples indicates that the high activity of calcium not only promotes the formation of sulfates (Ah and SO) from calcite (in the presence of sulfur and oxygen), but also the dehydration of gypsum during and after combustion, which occurs at temperatures above 400–500°C. It is very important to understand the interaction of high-calcium fly ashes with water occurring in Portland cement (C3A,C2S), Ah, which hydrates to give gypsum and lime, with the latter hydrating to give the Ca(OH)2 solutions that promote pozzolonic reactions. It was clear from the microscopy data that some of the particles comprised predominantly irregularly formed, vesicular particles with some well-formed individual spheres in Catalagzi and Tuncbilek fly ashes. About 55–80 wt% was less than 45 μm in size for Yatagan, Soma, Yenikoy and Afsin-Elbistan fly ashes. Chemical analyses of the fly ashes showed that they were mainly composed of CaO, SiO2 and Al2O3. These fly ashes have a potential use in wastewater treatment since they can be easily obtained in large quantities at low price or even without price. The chemical and mineralogical compositions of the high-calcium Turkish fly ashes investigated make them a good binding agent and a possible substitute for slags, pozzolana and gypsum in the amelioration of clinker. Moreover, the fly ashes could be also used as a liming material to raise the low pH of acid salts in humid regions, such as around the Black Sea coast of Turkey.

Bioleaching of Zinc and Iron from Steel Plant Waste using Acidithiobacillus Ferrooxidans

The bacterial leaching of zinc and iron from solid wastes at the Isdemir iron and steel plant has been investigated using Acidithiobacillus ferrooxidans as the bacterial agent. The effects of a range of operational parameters, including particle size, solids concentration and pH, on the efficiency of the bioleaching process were investigated. In each test, several variables were determined to assess the efficiency of leaching, including slurry pH and redox potential, temperature, bacteria population and concentrations of zinc and iron in solution. Experimental results demonstrated that pulp solids concentration, slurry pH and solids particle size were all important parameters in the bacterial leaching process. Maximum extraction was achieved at pH values around 1.3 and a solids concentration of 1% w/v, with 35% of the Zn content and 37% of the Fe being dissolved.

REMOVAL OF Fe FROM KAOLIN BY CHEMICAL LEACHING AND BIOLEACHING

The use of microorganisms to remove Fe (oxyhydr)oxides from kaolins has the potential to be an effective method for upgrading the whiteness and brightness, and therefore the commercial value, of the kaolin. The purpose of the present study was to compare kaolin products obtained by currently used chemical leaching methods with a bioleaching treatment using Aspergillus niger in order to remove Fe from kaolin (from Canakkale, Turkey). The effects of pulp density, temperature, and oxalic acid concentration on the chemical leaching experiments were investigated using the ANOVA-Yates test. The greatest degree of removal of Fe from the kaolin sample (at 15% w/v pulp density, temperature of 80°C, oxalic acid concentration of 0.2 M, and a particle size of <63 µm) was found to be 94.89% in 120 min of leaching. The Fe content decreased from 1.723%) Fe2O3 to 0.088% Fe2O3. In a shake flask, bioleaching of kaolin by Aspergillus niger resulted in removal of 77.13% of the total Fe, suggesting that this strain is effective at removing Fe impurities from kaolin. The removal efficiency generally decreased with increased pulp density. The Fe content of the kaolin decreased from 1.723% Fe2O3 to 0.394% Fe2O3 (at 1% w/v pulp density, temperature of 25°C, Aspergillus niger 3 × 107 spores, and particle size of <63 µm) after 21 days of bioleaching.

Effects of size distribution on flotation kinetics of Turkish sphalerite

Abstract The effects of size distribution on the flotation behaviour of sphalerite have been investigated in terms of kinetic parameters. In experimental studies, subsamples of a Turkish sphalerite ore were ground for different times using a laboratory ball mill. Timed batch tests were then undertaken using a pilot flotation column and the resulting recovery/time data were used in kinetic modelling. Results indicated that sphalerite floated rapidly at a medium particle size distribution (d80 = 0·125 mm in this case). In addition, a statistical analysis of data demonstrated that the flotation rate constant corresponded to a first-order model with rectangular distribution of floatabilities given by the equation: r = R∞(1-1/k 2 t[1-exp(-k 2 t]}

Application of a flocculation–ultrafiltration process for bacteria (Desulfovibrio desulfuricans) removal from industrial plant process water

The treatment of well-water containing bacteria (Desulfovibrio desulfuricans) used as process (cooling) water at the glass manufacturing plant in Mersin, Turkey has been studied in order to remove bacteria in suspension by coagulation/flocculation followed by ultrafiltration. Using a jar-test procedure, physico-chemical conditions have been optimised. Among the different types of additives investigated, a particular type of polyacrylamide (Magnafloc 1011, very high molecular weight anionic) resulted in a 65.22% bacteria removal from the well-water at a dosage of 0.01 g/l, while the combined use of flocculation and ultrafiltration methods achieved bacteria removal of 89.85% from the well-water.

Effects of oxidising agents on dissolution of Gumuskoy silver ore in cyanide solution

The aim of this research was to increase the silver extraction rate of the limonite-manganiferous silver ore from Gumuskoy, north western Turkey. The effects of the addition of oxidising agents (air, hydrogen peroxide and gaseous oxygen) on silver leaching were studied. The use of hydrogen peroxide mixed with air increased the rate of silver dissolution and also shortened the leaching time.

Emission Characteristics of Co-combustion of Sewage Sludge with Olive Cake and Lignite Coal in a Circulating Fluidized Bed

Abstract In this study, a circulating fluidized bed (CFB) of 125 mm diameter and 1800 mm height was used to find the combustion characteristics of sewage sludge (SS) produced in Turkey. Sludge + olive cake, and sludge + lignite coal mixtures were burned separately. Various sludge-to-lignite coal and sludge-to-olive cake ratios (5/95, 10/90, 15/85, 20/80) were tried. On-line concentrations of major components (O2, SO2, CO2, CO, NO x , C m H n ) were measured in the flue gas, as well as temperature and pressure distributions along the bed. Combustion efficiencies of sludge + olive cake and sludge + lignite coal mixtures were calculated, and the optimum conditions for operating parameters were discussed. The results have shown that the combustion mainly takes place in the upper regions of the main column where the temperature reaches 900°C. SS + Coal burn in the CFB with an efficiency of 95.14% to 96.18%, which is considered to be quite good. When burning sludge mixed with olive cake, appreciable amounts of CO and unburned hydrocarbons are formed and the combustion efficiency drops to 92.93%. CO and C m H n emissions are lower when lignite coal is mixed with various amounts of SS than the emissions when the coal is burned alone. As the %SS is increased in the fuel mixture, the SO2 emission decreases. NO x emissions are slightly higher. When burning sludge mixed with olive cake, SO2 and NO x emissions are slightly higher. CO and C m H n emissions decrease sharply when SS is mixed with 5%wt. olive cake. With increasing sludge ratio these emissions increase due to the unburned hydrocarbons. As a result of this study, it is believed that SS can be burned effectively in a CFBC together with other fuels, especially with olive cake (OC). OC will be a good additive fuel for the combustion of lower quality fuels.

Desulfurization of High Rank Coal (TKI-Husamlar, Mugla, Turkey) using Humic Acid

Oxides of sulfur created when coals are burned have been recognized as a real threat to both the ecosystem and human health with regard to the environmental aspects. Turkish lignites usually contain a high percentage of ash and both organic and inorganic sulfur. The ash and sulfur contents can be reduced using physical-chemical and chemical methods. Desulfurization of a high rank coal (TKI-Husamlar, Mugla, Turkey) with total sulfur of 3.65 % was extracted using humic acid. Effects of reaction time and temperature on the removal of sulfur were investigated using 10 %wt. humic acid. The leaching reaction time was ranged from 15 to 60 minutes with an interval of 15 minutes. It was determined that the highest sulfur removal (57.70 % of total sulfur) with 17.78 % ash removal and 81.15 % coal yield were achieved at 90 °C with 45 minutes of reaction time using 10 %wt. humic acid with −1 mm high rank coal.