Comparison of CO2 capture by ex-situ accelerated carbonation and in in-situ naturally weathered coal fly ash

Natural weathering at coal power plants ash dams occurs via processes such as carbonation, dissolution, co-precipitation and fluid transport mechanisms which are responsible for the long-term chemical, physical and geochemical changes in the ash. Very little information is available on the natural carbon capture potential of wet or dry ash dams. This study investigated the extent of carbon capture in a wet-dumped ash dam and the mineralogical changes promoting CO2 capture, comparing this natural phenomenon with accelerated ex-situ mineral carbonation of fresh fly ash (FA). Significant levels of trace elements of Sr, Ba and Zr were present in both fresh and weathered ash. However Nb, Y, Sr, Th and Ba were found to be enriched in weathered ash compared to fresh ash. Mineralogically, fresh ash is made up of quartz, mullite, hematite, magnetite and lime while weathered and carbonated ashes contained additional phases such as calcite and aragonite. Up to 6.5 wt % CO2 was captured by the fresh FA with a 60% conversion of calcium to CaCO3 via accelerated carbonation (carried out at 2 h, 4Mpa, 90 o C, bulk ash and a S/L ratio of 1). On the other hand 6.8 wt % CO2 was found to have been captured by natural carbonation over a period of 20 years of wet disposed ash. Thus natural carbonation in the ash dumps is significant and may be effective in capturing CO2.Web of Scienc

Monitoring nutrient¯ows and economic performance in African farming systems (NUTMON). III. Monitoring nutrient¯ows and balances in three districts in Kenya

Abstract A nutrient balance study was carried out for 26 farms in three different districts in Kenya. Balances for the major nutrients nitrogen, phosphorus and potassium were calculated for individual activities within the farms and for the entire farms, using Farm-NUTMON, a research tool that combines calculation of nutrient¯ows and balances with economic farm analysis. Four ows into the farm (chemical fertilizer, organic fertilizer and feeds, atmospheric deposition, nitrogen ®xation), six¯ows out of the farm (farm products, other organic outputs, leaching, gaseous losses, erosion and human excreta) and six internal¯ows (consumption of external feeds, household waste, crop residues, grazing, animal manure, and home consumption of farm products) were considered. Data on fertilizer use, use of organic materials, yields, home consumption and the management of residues, manure and household waste were gathered by interviewing the farmer. Assumptions for deposition, leaching and gaseous losses were made by using empirical relationships based on literature data (transfer functions). Erosion was estimated relating the overall slopes of the farms to soil loss ®gures. The mean balance of all farms was À71 kg N, 3 kg P and À9 kg K ha À1 yr À1 , with large variations between farms and little variation between districts. Emissions (leaching, gaseous losses and erosion) were estimated to be much higher than immissions (atmospheric deposition and N-®xation). In¯ows and out¯ows at ®eld level were much higher for cash crops than for food crops. Soil nutrient mining under napier grass (Pennisetum purpereum) was severe from high estimated losses in the napier-livestock-manure cycle. Based on an evaluation of the results of this case study, recommendations were made for improvement to the approach. Developing a sustainability indicator for soil fertility requires the nutrient balance to be linked to the actual soil nutrient stocks and other soil quality indicators.

Synthesis and characterization of hydrotalcite from South African Coal fly ash

The synthesis of adsorbents such as hydrotalcites (HT) from mineral waste (e.g. blast furnace slag) is receiving increasing attention. This study reports a novel procedure to prepare HT from a South African coal-combustion fly ash, an ubiquitous waste generated by coal-fired power stations. The second point of novelty is the optimization process, which highlights the boundary conditions for crystallization of this mineral phase. The parameters investigated for the optimization of HT synthesis from fly ash included HCl concentration, aging time and temperature, pH during the aging step, and crystallization time and temperature. The most suitable synthesis conditions were: HCl concentration of 3 M, aging time of 30 min, aging temperature of 65 °C, pH of 11.5 during aging, crystallization time of 12 h, and crystallization temperature of 70 °C. HT had a large external surface area and very low microporosity. Morphologically, synthesized HT was mostly made up of sub-micron plate-like particles. The structural characteristics of HT synthesized from fly ash were similar to those of HT produced from analytical grade chemicals, except for the presence of calcite. A novel use of the waste South African Class F fly ash was a suitable feedstock for the synthesis of high quality HT under the optimized process conditions that minimized the formation of secondary undesired mineral phases such as calcite or hydrogarne

Response of potato crop to selected nutrients in central and eastern highlands of Kenya

Low nutrients have been reported in potato-growing areas of Kenya, prompting a need for nutrient management research. A study was designed to determine the effect of omitting nutrients on potato growth, yield and harvest index. On-farm nutrient omission trials were set during the long rains (LR) and short rains (SR) of 2016 in which the treatments involve the judicious omission of N, P, K, S and B. Additional two treatments were included with one receiving all the nutrients and a control where no nutrients were added. The treatment was laid in a randomized complete block design with three replications. Potato yields reduced by 6.6 and 11.2 t ha−1 in N-omitted treatments in LR and SR, respectively, when compared to the one receiving all the nutrients, while omitting P resulted in respective yield reductions of 3.8 and 2.0 t ha−1. Stability analysis revealed that omission of N was more stable with a regression coefficient of 0.5; it was followed by P with a value of 1. Potassium, S and B were limiting nutrients only in some farms. N and P should continue to be included in potato nutrient management, while K, S and B should be added based on soil test

Turning biennial into biannual harvest: Long-term assessment of Arabica coffee–macadamia intercropping and irrigation synergism by biological and economic indices

Intercropping that involves coffee (Coffee arabica L.) and macadamia (Macadamia integrifolia Maiden & Betche) can achieve the complementarity between component crops aiming at better use of natural resources, hence resulting in optimum crop production. However, there is no detailed information in the scientific literature about the biological and economic efficiency of coffee–macadamia intercropping. In this work, we evaluated the productivity and economic performance of Arabica coffee–macadamia intercropping under rainfed and irrigated conditions for 13 years (2006–2018) in São Paulo state, southeastern Brazil. In addition, some biological, economic, and competition indices were used to understand the complementarity of companion crops under the intercropping system. Irrigation significantly increased coffee (21%–40%) and macadamia (33%–44%) yields. Despite the greater values of aggressivity and dominance indices of macadamia over coffee crop have been calculated in the rainfed regime, intercropping with macadamia reduced more strongly coffee yield under irrigation. The higher values of land equivalent ratio (LER), land equivalent coefficient (LEC), percentage yield difference (PYD), income equivalent ratio (IER), and relative net return index (RNRI) indicated relatively higher benefits of intercropping under rainfed regime than under irrigation. The intercropping systems were more productive than monocrops, reaching 215% more yield, 3.2-fold more gross income under rainfed conditions. The synergy of the combined use of irrigation and intercropping technologies decreased the payback period and the highest values of coffee equivalent yield (CEY) and monetary advantage index (MAI) under irrigation indicated a cumulative effect on the profitability. Here, for the first time, we demonstrated the complementarity between Arabica coffee and macadamia under the intercropping system, at least up to 13 years after planting of the crops, and suggest that it may be a viable option to optimize the use of resources, food production, and ecosystem services, making agricultural profitability more sustainable and stable.Department of Crop Science College of Agricultural Sciences São Paulo State University (UNESP)São Paulo Agency of Agribusiness Technology (APTA/SAA) Midwest RegionalDepartment of Agricultural Sciences and Technology School of Agriculture and Enterprise Development Kenyatta UniversityDepartment of Crop Science College of Agricultural Sciences São Paulo State University (UNESP

Antimalarial Pyrido[1,2-a]benzimidazoles

A novel class of antimalarial pyrido[1,2-a]benzimidazoles were synthesized and evaluated for antiplasmodial activity and cytotoxicity following hits identified from screening commercially available compound collections. The most active of these, TDR86919 (4c), showed improved in vitro activity vs the drug-resistant K1 strain of Plasmodium falciparum relative to chloroquine (IC(50) = 0.047 muM v 0.17 muM); potency was retained against a range of drug-sensitive and drug-resistant strains, with negligible cytotoxicity against the mammalian (L-6) cell line (selectivity index of <600). 4c and several close analogues (as HCl or mesylate salts) showed significant efficacy in P. berghei infected mice following both intraperitoneal (ip) and oral (po) administration, with <90% inhibition of parasitemia, accompanied by an increase in the mean survival time (MSD). The pyrido[1,2-a]benzimidazoles appeared to be relatively slow acting in vivo compared to chloroquine, and metabolic stability of the alkylamino side chain was identified as a key issue in influencing in vivo activit