The removal of zinc from contaminated dredged-sediments

Dredged-sediments increased to about 15million m2 from 1998 to 2012 by port construction, sediment reclamation and dredging business. Most of dredged-sediments which are generated in Korea have been treated by Marine dumping. However, there are increasing concern about contamination by heavy metals in dredged-sediments. Therefore, it is required to remove heavy metals from dredged-sediments. The purpose of this study is to remove zinc from domestic dredged sediments contaminated with ZnS using ferric chloride. Consequently, leaching behavior of zinc was investigated under the following leaching conditions400rpm, 80℃ and 0.5M FeCl3 in 1M HCl, and content of zinc in residue decreased to 184mg/kg which meet Marine dumping regulations(Zn:200mg/kg). The shrinking core model(Ash diffusion controlled) was investigated based on the leaching results. Correlation coefficients were closed to 1 so that model best fitted to the kinetic data. The activation energy for the leaching process was found to be 64.1-76.9kJ/mol for 1-0.25M FeCl3 respectively, and that means leaching precess depends on chemical reaction.40 and 90℃ in temperature, 0.25-1M in concentration of ferric ion, 5-20% in pulp density, and 200-600rpm in stirring speed. Leaching efficiency of zinc increased with leaching temperature and ferric ion concentration. The leaching efficiency was 96.7% under the following conditions제 1 장. 서 론 1 1.1 개요 1 1.2 연구사례 7 1.2.1 3가 철 이온의 특징 7 1.2.2 침출연구사례 7 제 2 장. 이론적 배경 11 2.1 열역학적 해석 11 2.2 속도론적 해석 13 제 3 장. 침출거동 확인 19 3.1 사용시료 19 3.2 실험방법 19 3.3 실험결과 22 3.3.1 교반속도에 따른 침출거동 22 3.3.2 Fe3+ 농도에 따른 침출거동 24 3.3.3 광액비 변화에 따른 침출거동 25 3.3.4 온도변화에 따른 침출거동 27 제 4 장. 속도론적 해석결과 31 4.1 Shrinking core model (Film diffusion controlled) 31 4.2 Shrinking core model (Reaction controlled) 35 4.3 Shrinking core model (Ash diffusion controlled) 39 4.4 Dickinson and Heal model 42 4.5 활성화 에너지(Activation energy) 47 제 5 장. 결론 50 참고문헌 52 감사의 글 5

Experimental studies on the generation and evolution of mineral porosity during fluid-mediated mineral replacement reactions

The porosity in minerals contributes to enhanced permeability for fluid flow in natural systems and engineering processes. Porosity can be created by fluid-mediated mineral replacement reactions. Such reaction-induced porosity can evolve with time, yet the mechanisms and kinetics of porosity creation and evolution remain poorly understood. This thesis presents experimental investigations on the creation and evolution of mineral porosity in two model replacement reactions, i.e., the replacement of calcite by gypsum and anhydrite with a positive volume change and the replacement of pentlandite by violarite and millerite with a negative volume change. These replacement reactions were conducted under mildly acidic hydrothermal conditions for up to 18 months, and the mineralogy, microstructure and porosity of the reaction products were quantitatively analysed by powder X-ray diffraction, (ultra) small-angle neutron scattering, high resolution scanning electron microscopy, focused-ion beam scanning electron microscopy, and X-ray micro-tomography. The results showed that porosity creation and evolution are highly dependent on mineral systems and reaction conditions. In the calcite-gypsum-anhydrite mineral system, the experiments at 25-60 °C produced intragranular nanopores in gypsum replacing calcite. Because of the positive volume change, gypsum overgrowth also occurred on the grain surface, and the gypsum in the overgrowth region contained intergranular micropores. Porosity coarsening was rapid (a few weeks) in the replacement region, leading to the formation of micro-voids in the core of gypsum grains. The replacement reaction was sensitive to temperature. When the experiments were conducted at a higher temperature of 220 °C, anhydrite was formed instead of gypsum. Porosity evolution in anhydrite was different when compared to gypsum at lower temperatures. In the pentlandite-violarite-millerite mineral system, only replacement occurred, likely because the negative volume change does not require overgrowth for additional space. The replacement was sensitive to temperature and solution pH. The experiments conducted at 125 °C and pH 4 produced permeable nanopores leading to the complete replacement of pentlandite; these nanopores coarsened slowly during the 17 months of experiment and occurred preferentially near the grain surface. However, in experiments conducted at 125 °C and pH 5, violarite became impermeable in partially replaced grains due to hematite precipitation in the pore space, blocking the fluid flow. At a higher temperature of 220 °C and pH 4, the formation of millerite in addition to violarite resulted in faster porosity coarsening and formed micropores within 4 weeks. Fundamentally, these complex porosity creation and evolution phenomena observed in the two model mineral replacement reactions are controlled by the interplay between dissolution, precipitation, epitaxial nucleation, and Ostwald ripening processes which are all sensitive to reaction conditions. This understanding should generally be applicable to other mineral replacement reactions. Finally, a case study of the application of porosity control was presented. The leaching of chalcopyrite is often kinetically inhibited by surface passivation layers, which are formed by the replacement of chalcopyrite during leaching. Common passivation layers are elemental sulphur and jarosite. Our leaching experimental results showed that surface sulphur could be removed by adding sulphur-dissolving solvent tetrachloroethylene (TCE) into the sulfuric acid leaching solution. The removal of surface sulphur significantly improved the leaching rate by almost 6 times compared with TCE-free leaching. At the later stage of leaching, chalcopyrite was replaced by potassium jarosite. The jarosite shell did not passivate TCE-free leaching due to its porous structure. However, the jarosite shell became nearly impermeable in TCE-assisted leaching because elemental sulphur filled the pores in the jarosite. This case study suggests that chalcopyrite leaching can be significantly enhanced by either removing the surface passivating layer or by controlling the porosity and permeability of the surface layers formed on the chalcopyrite surface

Towards a circular economy: fabrication and characterization of biodegradable plates from sugarcane waste

Bagasse pulp is a promising material to produce biodegradable plates. Bagasse is the fibrous residue that remains after sugarcane stalks are crushed to extract their juice. It is a renewable resource and is widely available in many countries, making it an attractive alternative to traditional plastic plates. Recent research has shown that biodegradable plates made from Bagasse pulp have several advantages over traditional plastic plates. For example, they are more environmentally friendly because they are made from renewable resources and can be composted after use. Additionally, they are safer for human health because they do not contain harmful chemicals that can leach into food. The production process for Bagasse pulp plates is also relatively simple and cost-effective. Bagasse is first collected and then processed to remove impurities and extract the pulp. The pulp is then molded into the desired shape and dried to form a sturdy plate. Overall, biodegradable plates made from Bagasse pulp are a promising alternative to traditional plastic plates. They are environmentally friendly, safe for human health, and cost-effective to produce. As such, they have the potential to play an important role in reducing plastic waste and promoting sustainable practices. Over the years, the world was not paying strict attention to the impact of rapid growth in plastic use. As a result, uncontrollable volumes of plastic garbage have been released into the environment. Half of all plastic garbage generated worldwide is made up of packaging materials. The purpose of this article is to offer an alternative by creating bioplastic goods that can be produced in various shapes and sizes across various sectors, including food packaging, single-use tableware, and crafts. Products made from bagasse help address the issue of plastic pollution. To find the optimum option for creating bagasse-based biodegradable dinnerware in Egypt and throughout the world, researchers tested various scenarios. The findings show that bagasse pulp may replace plastics in biodegradable packaging. As a result of this value-added utilization of natural fibers, less waste and less of it ends up in landfills. The practical significance of this study is to help advance low-carbon economic solutions and to produce secure bioplastic materials that can replace Styrofoam in tableware and food packaging production