Utilization of fly ash for treatment of coal mines wastewater: Solubility controls on major inorganic contaminants

Acid mine drainage (AMD) has been reacted with coal fly ash in a 24 h equilibration time using 1:3 and 1:1.5 FA:AMD ratios by weight to produce neutral and alkaline process waters. The capacity of the fly ash to remove the major inorganic contaminants was examined. The elemental concentration trends with time for the two ratios were used to discern which elements have solubility control in the neutralization process. The geochemical computer code PHREEQC and WATEQ4 database was used for geochemical modeling of the process water. The resulting solid residues (SR) were analyzed by X-ray diffraction (XRD), and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDX) in an attempt to detect the minerals phases controlling the inorganic contaminants concentration in solution. The relative quantities of soluble bases (CaO, MgO) in fly ash and hydrolyzable constituents in AMD dictated whether the final solution at a given contact time will have a dominant acidic or basic character. Concentration of Fe, Al, B were observed to be controlled by mineral solubility for the entire reaction time while mineral solubility control for Ca, Na, Mg, Si and Mn concentrations developed after the initial rapid dissolution. Initial concentration was controlled by precipitation of gypsum and adsorption on iron-oxy-hydroxides at pH > 5.5. Increase of pH in solution with contact time caused the removal of the metal ions mainly by precipitation, co-precipitation and adsorption. Fe was mainly removed as Fe(OH)_3(a), goethite, Al as basaluminite, boehmite and alunite at pH 5.28-6.95 and as gibbsite and diaspore at pH 5.53-9.12. Cu and Zn were removed by adsorption onto the precipitating iron(oxy)-hydroxides and aluminum (oxy)-hydroxides. Si is released by dissolution of SiO_2(a) at pH < 5. Na was removed as Na-jarosite at pH 3.96-6.95 and Ca as gypsum and anhydrite. The treatment of AMD with fly ash was observed to be site-specific, i.e., the effectiveness of the treatment process will depend on the quality of the fly ash and the AMD. The product water meets the DWAF water quality limits for domestic use and irrigation at pH > 8 except for species Na, B, Mg, Ca, Sr and Ba which remain in solution. In addition B, Mg, Sr, Mo and Ba are released from dissolution of fly ash and will be of concern in the proposed treatment process.     

An inquiry into the integration of indigenous knowledges and skills in the Kenyan secondary science curriculum: A case of human health knowledge1

Abstract

In this paper I compare and contrast portions of the Kenyan biology syllabus (Kenya National Examinations Council [KNEC], 1990) with knowledge and skills in the area of health and healing in a rural part of Kenya—Kirumi. The purpose of the interpretive study on which the paper is based was to ascertain the status of indigenous knowledges and skills in the Kenyan high school science curriculum. This purpose results from a long‐standing plan by the Kenyan government to indigente2 the entire curriculum. In particular, I focused on the topic called Human Health in a Form 4 (Grade 12 equivalence) biology text (Kenya Institute of Education, 1989). The textbook was at the time one of the set books endorsed by the Ministry of Education as a syllabus guide. Then, through grounded theory method, I identified the principles and processes that underlay knowledges and skills in the area of health and healing in Kirumi. Following that, I used these principles and processes as the basis for a critique of the Human Health topic. My findings showed that the Kenyan biology syllabus, despite the plan to indigenize, does not take cognizance of indigenous principles of health and healing. Consequently, the socio‐cultural, environmental, and emotional dimensions of health are omitted; health is portrayed as the responsibility of experts and not the self; and herbs and diet are omitted as measures for creating a healthy body. The findings showed an overall disparity between the biology text and rural knowledges and skills in the area of health and healing. The findings have alarming implications, because when many of the students end their schooling, they will require indigenous knowledges and the associated skills in order to make positive epistemological contributions to the rural community. My study builds upon published research that shows the importance for effective knowledge transfer of integrating everyday knowledges and skills into curricula. However, there is lacking in this literature a systematic investigation of the status of such knowledges and skills in existing curricula. My argument is that it is important to highlight systematically the disparities between school offerings and everyday offerings in order to provide substantive materials for integration. In the absence of such materials, educators work with artefacts. For instance, in the Kenyan high school biology syllabus there is a casual mention, in the name of integration, of the benefits that cultural foods confer on health. Whereas artefacts may help to illustrate indigenous experiences, they do not systematically and openly challenge the underlying belief systems that have over time marginalized the epistemological value of indigenous knowledges and skills.     

Optimizing soil nitrogen balance in a potato cropping system through legume intercropping

Nutrient Cycling in Agroecosystems - Negative nitrogen balance represents a major factor causing low potato yield in potato growing areas of Kenya while its excessive surplus poses a significant...     

Fate of sulphate removed during the treatment of circumneutral mine water and acid mine drainage with coal fly ash: Modelling and experimental approach

The treatment of acid mine drainage (AMD) and circumneutral mine water (CMW) with South African coal fly ash (FA) provides a low cost and alternative technique for treating mine wastes waters. The sulphate concentration in AMD can be reduced significantly when AMD was treated with the FA to pH 9. On the other hand an insignificant amount of sulphate was removed when CMW (containing a very low concentration of Fe and Al) was treated using FA to pH 9. The levels of Fe and Al, and the final solution pH in the AMD–fly ash mixture played a significant role on the level of sulphate removal in contrast to CMW–fly ash mixtures. In this study, a modelling approach using PHREEQC geochemical modelling software was combined with AMD–fly ash and/or CMW–fly ash neutralization experiments in order to predict the mineral phases involved in sulphate removal. The effects of solution pH and Fe and Al concentration in mine water on sulphate were also investigated. The results obtained showed that sulphate, Fe, Al, Mg and Mn removal from AMD and/or CMW with fly ash is a function of solution pH. The presence of Fe and Al in AMD exhibited buffering characteristic leading to more lime leaching from FA into mine water, hence increasing the concentration of Ca²⁺. This resulted in increased removal of sulphate as CaSO₄·2H₂O. In addition the sulphate removal was enhanced through the precipitation as Fe and Al oxyhydroxysulphates (as shown by geochemical modelling) in AMD–fly ash system. The low concentration of Fe and Al in CMW resulted in sulphate removal depending mainly on CaSO₄·2H₂O. The results of this study would have implications on the design of treatment methods relevant for different mine waters.     

Exploring the Understanding and Common Use of Scientific and Everyday Knowledge and Students’ Agency in a Kenyan High School

Abstract

The understanding and applications of scientific and everyday knowledge by high school students was documented among 52 secondary students in Kenya. The study utilized a socio-cultural framework, a pre- and post-data-collecting strategy, and theme building in data analysis. Posttest data showed an increase of claims that referred to the conduct of scientific inquiry or systematic “finding out.” It appears that the content of the lecture prompted students’ to consider using scientific knowledge to solve problems in everyday life. The implications of the study point to a reconsideration of the practices of science education in Kenya and similar contexts.     

Visitor perspectives on the nature and practice of science: Challenging beliefs through a question of truth

Abstract

A trademark of science centres around the world is that they often develop their exhibits around a scientific phenomenon (i.e., light, sound, gravity). However, the exhibit A Question of Truth, located at the Ontario Science Centre, examines several questions about the nature of science itself, how ideas are formed, and how cultural and political conditions affect the practice of science. A Question of Truth extends the visitor experience to include discussion and interaction around the sensitive themes of bias in science and society; points of view; and science and race. Specifically, this study asks the following questions: (a) What are visitors’ understandings of the nature and practice of science in the context of a museum exhibition that aims to situate science in social, cultural, and political milieus? (b) What are visitors’ responses to A Question of Truth, paying particular attention to what they found surprising, challenging, and disturbing? Observation and interview data indicate that science centre visitors are interested in considering science and the sociocultural context in which it operates. Visitor support for this type of exhibit challehges traditional, rule‐bound views and representations of science. The paper concludes with several implications for science centres and science education.