Recyclable materials have increased in prevalence due to various technical, economic, society and environmental reasons. These materials need allow us to manage resources and with less harm to the environmental. The purpose of this course is to broaden the intellectual discourse and bring attention to various aspects of materials recycling. Therefore, this recycling course called “Introduction to Recycling of Materials” at Worcester Polytechnic Institute (WPI), and taught is Fall 2018. These lectures focus upon the on basic characterization and separation techniques of recyclable materials, recycled products, environmental concerns, and commercial applications. After each lecture, students are expected to gain an understanding of recycling concepts and processing techniques.
Student Course Objectives: At the end of term the student should be able to:
- To understand and apply the extractive metallurgical fundamentals, processes and principles in the hydrometallurgical treatment of recycled materials;
- To understand the current state of art in recycling technologies;
- To understand the meaning and value of recycling;
- To use creative thinking to develop new possibilities for recycling;
- To understand the fundamental principles for the characterization of recyclable materials;
- To utilize standard analytical techniques;
- To understand the fundamentals of separation and purification of recyclable materials;
- To learn and utilize relevant physiochemical processes and economic analysis;
- To demonstrate written communication skills;
- To understand to understand the types of impacts and as well as environmental impact assessment and understand how it could impact mining and recycling.
Recycling is the process of collecting, sorting, separating and purifying recyclable materials and while minimize what would have previously been called waste and processing it into new materials. Recycling includes various metals and alloys as well as some plastics, glasses, woods, paper and e-scrap from TV, cellphones and computer. Some of the valuable metals in these products include include, copper, aluminum gold, silver, platinum and steel. However, these products contain harmful products such as mercury, cadmium, arsenic, and lead. These toxics can negatively impact the air, soil and water can lead to environmental and health problems.
Mercury is very dangerous liquid metal since body easily absorbs it via skin contact or inhalation, and can result in serious damage to the central nervous and reproductive systems, as well as irreversible neurological and kidney failures. Like mercury, lead and cadmium are also stored in the fatty tissues, kidneys and/or liver, and have similar side effects on people of every age, animals and other living organisms . Some of the side effects of these hazardous materials remain hidden, and cannot be detected by a clinical examination. In addition to these materials, there are a number of organic substances (e.g., chlorofluorocarbon, halogenated compounds and trichloroethylene) that are heavily utilized by the industry and cause birth defects, miscarriages and other long term mental and physical illnesses [1-3]. In this class, students learn all the health issues of these toxic and hazardous materials and their handelabilities in detail.
Recycling saves our environment and future by reducing greenhouse gas emissions, soil contaminations, and air and water pollutions, conserving natural resources and energy, and increasing economic value and job opportunities. There are four main impacts of recycling of materials and devices that students learn in this class:
By reducing the amount of used energy by industry, recycling reduces greenhouse gas emissions and global climate change. Most of the energy used in industrial processes and in transportation is produced by burning fossil fuels, such as gasoline, diesel, coal and other carbon associated sources [1-3]. A new study shows that even 1 degree Celsius increase in temperature by carbon dioxide or other green house gasses (e.g., methane) will cause thousands of deaths and respiratory illnesses in the U.S. . In order to minimize these unwanted emissions and slow global warming, recycling rates need to be increased worldwide. Additional benefits of recycling are to reduce emissions from incinerators and landfills, and slow the harvest of trees. Soils contaminated by leaching of lead, mercury and other unwanted heavy metals (zinc, tin, cobalt, chromium and cadmium) and their compounds, as well as biologic and nuclear waste materials poses significant health risks to large populations in the world. This is because the contaminated soils will eventually contaminate the agricultural products and other feedstock, and hence poison human and animals in the long term. Current methods used to lower the soil contaminations are too expensive and time consuming for large-scale applications [1,6]. Thus, it is highly recommended to recycle all the materials before sending to landfills and other collection areas. After those unwanted materials interact with the ground, it will take longer time to clean completely.
Recycling can reduce air pollutants, as well [1,6]. Suspended particles in air have a complex mixture of extremely small particles and liquid droplets. The big particles are in the range of 2.5 to 10 µm, whereas the small particles are below 2.5 µm. Particulate pollution consists mainly of a number of components, including acids (nitrates and sulfates), organic chemicals, metals, and soils or dust particles. The largest natural sources of particles are wind-blown dust, volcanoes and forest fires, while the largest human sources of particles are combustion sources, mainly coming from the burning of fossil fuels, internal combustion engines in transportation vehicles, and other coal and natural gas powered stations. Figure 1 shows the sources of particulate matters in the air.
In addition to greenhouse gas emission and soil and air contaminations, drinking water supplies, such as rivers, lakes and underground water can be contaminated by various sources, which is one of the biggest threats to human being now [1,6]. Instead of obtaining raw materials by mining operations, recycling can eliminate the pollutions associated with material extraction, refining and processing. Mining activities and other manufacturing operations can pollute water resources with toxic materials (e.g., highly acidic and basic solutions, polymers, surfactants, solvents and electrolytes). Also, carbon, sulfur and nitrogen gases can interact with water droplets in air of the atmosphere and return as acid rain (e.g., sulfuric acid, carbonic acid and nitric acid), which directly affect the vegetation, human and animals, as well as increase the corrosion and degradation rates of metals and alloys, polymers, composites and woods [7-9]. This is part of atmospheric corrosion and degradation (Figure 2), which can completely change the properties of materials and destroy them in the long term [9,17].
Recycling generates significant economic benefits in the region. The recycling of used materials reduces the consumption of raw materials, and other unwanted emission and contaminations as compared to virgin production [1-3]. The creation of secondary raw materials via the recycling route also expends far less energy than a production based on primary raw materials. Table 3 gives the energy savings of various recycled materials .
It is estimated that recycling and related remanufacturing industries create over a million jobs and more than $100 billion of revenue in the U.S. [1,10]. Recycling employs all levels of workers from low to high in a wide variety of jobs, including collection, transportation, characterization, separation, processing, new product development and manufacturing, storage and marketing. Many government agencies (e.g., environmental protection agency) in the U.S. provide technical assistance and funds to recycling businesses in all stages. Investments in recycling facilities, equipment and devices contribute to a long term economic growth. Also, using recycled materials and devices will enhance the sustainability and reliability of future products that customers can use without any hesitation or concerns.
Like recycling, educational development is of great interest in every major or discipline [18-20]. Recycling education is being offered by many universities as an option or required course in the U.S.A. and around the world. Generally, it involves a multidisciplinary engineering and science education in materials science, chemistry, mechanical, chemical, environmental and electrical engineering. There are also recycling centers and programs in government agencies and private companies that are dedicated to research, development and outreach services for the students, local community and industry by offering courses, seminars, workshops and forums [1-3]. It is believed that research and development in recycling will likely change the traditional design, analysis, and manufacturing methods to produce a wide range of recycled products.
Recycling activities around the world promote community development and social interactions. The other implications include increased lifespans made possible through a cleaner environment; safer working conditions for employees; increased citizens’ interests seeking employment or volunteer work; and improved scientific, cultural and other activities nationally and internationally.
Sources of waste mainly include chemical, mines and quarry, food, nuclear, pharmaceutical, textile and dye-works, petrochemical, pulp and paper mills, iron steel, automobile and agricultural industries, as well as household, schools, hospitals and car-wash stations . Waste minimization is a process and policy of reducing the amount of the toxic hazardous waste. In order to reduce the waste, several strategies have been developed and used worldwide, some of which are listed below [1-4]:
- Source Reduction: One of the most desirable methods of waste minimization is to reduce the source used for various purposes, which also reduces the impact of the wastes on the environment and health.
- Recycling: Another approach is to reduce the waste through recycling. A waste material is collected, treated and reused in the same or other processes. Recycling promotes the sustainable and long term use of our limited natural resources.
- Treatment: The most common method of treatment is to neutralize the waste using chemical, physical and/or biological methods. This will minimize the toxicity of the waste materials.
- Composting: Composting is an aerobic decomposition of biodegradable organic matter that can be done both on and off site, which will reduce the amount of mass to landfills and increase the farming production.
- Donation: Unspoiled food and clothes can be donated to local food banks, soup kitchens, and shelters. Local and national programs usually offer free pick-up and provide reusable containers. Fats and meat products can be used as raw materials in the rendering industry, which converts them into animal food, cosmetics, soap, and other valuable products.
- Methane Production: Food and other organic wastes can be recycled to produce methane gas in a controlled environment for energy production. Uncontrolled methane gas causes climate change and is 21 times more potent than carbon dioxide .
A number of different wet and dry methods have been developed to separate recyclable materials from the general waste stream. Dry methods include hand sorting, dry screening, magnetic, eddy current, electrostatic, optical, air cyclone, pneumatic separations and burning / firing, while wet methods include wet screening, gravity, heavy media, hydrocyclone, centrifugal separations, flotation, and bacterial and acid leaching. Based on the materials properties, size and shape, one or more of these methods are chosen to separate valuable materials [1-3]. When a smaller size separation is needed, waste materials can be crushed, ground and classified in different size fractions, and then sedimentation, filtration, dewatering and/or thermal drying steps take place. Figure 3 shows eddy current and rare earth magnetic separation methods currently employed be the recycling industry [1-6].
The present course, “Recycling of Engineering Materials”, is a three credit hour course at 600 level, and meets twice a week for 75 minutes each meeting time during the 14-week semester. This serves as an elective for the students in the Department of Mechanical Engineering and other College of Engineering’s senior and graduate level students at WSU. Two books are recommended for the present course, which are given below. In addition to these books, we also prepared and posted our own PowerPoint lecture notes on blackboard using information in the books and other sources.
Because of the enormous potential of recycling and its impacts, such as environmental, economical and stoical, Recycling of Engineering Materials course has been developed in the Department of Mechanical Engineering at WSU and taught in Spring 2008. It was a three credit hour course and met twice a week for 75 minutes during the 14-week semester. This improved the fundamental and practical knowledge of the students on how to collect, characterize, separate, reprocess and use the recyclable materials economically and efficiently. A course project has also been developed to apply knowledge learned in the course to design a creative recycling process. Students also realized that without recycling the waste materials, they would get corroded or degraded and completely destroyed by the nature, which would be a waste of resources and environmental damages.