Woo-Zin Choi

Influence of Metal Cations on Cassiterite Flotation

ABSTRACT Rotation of cassiterite has been studied on pure minerals in a microflotation cell with sulphosuccinamate as a collector in the presence of some metal ions. The results indicate that sulphosuccinamate demonstrates strong collection, good selectivity on cassiterite, especially in the weak acidity region of pH 6.0, and that lead ions have certain activation whereas other metal ions such as ferric, aluminum, manganese, ferrous, and calcium cause strong depression on cassiterite flotation. In addition, X-ray photoelectron spectroscopy (XPS) has been applied to study the flotation mechanism of cassiterite-sulphosuccinamate in the presence or absence of metal cation. A chemisorption mechanism through chemical bonding between stannum species on the cassiterite surface and oxygens from carboxylic and sulphonic acid groups of sulphosuccinamate is considered. The chemical environment of stannum species would be changed in the presence of lead ions in the flotation systems and improve the activity of the st...

Removal of PVC from Mixed Plastic Waste by Gravity Separation Process

ABSTRACT Plastics recycling has become an established national industry in Korea. However, it is still in its infant stage and experiences growing pains. Mixed plastic waste generated from households after hand picking and/or mechanical sorting processes amounts to 870,000 ton per year in Korea and most of them are finally end up with landfill and/or incineration due to lack of separation technologies and economical reasons. These plastic waste can not be used as raw materials for chemical and/or thermal recycling because of its high content of PVC (upto 4.0 wt.%). In the present work, gravity separation system has been developed to remove PVC from the mixed plastic waste. The separation system consists of air separation unit, shredding/grinding units, feeder, density separator, de watering units, pulp separator, plastic recovery system, wastewater treatment system, etc. The main objective of this process to be developed is to achieve high separation efficiency of polyolefins (PE, PP, PS) with less than 0.3 wt.% PVC content and less than 10% moisture content in the final products. The system with a capacity of 0.5 ton per hour is developed and operational results are presented.

Cassiterite Flotation with Sulphosuccinamate Collector

ABSTRACT Sulphosuccinamate is one of the best collectors used for flotation of cassiterite. The flotation results show that sulphosuccinamate displays strong collection and selectivity for cassiterite at lower dosage. The influence of other factors, such as depressants and metal cations on the cassiterite flotation has also been investigated. Studies on the mechanism of flotation with sulphosuccinamate, through zeta potential, infrared spectrometer, XPS and molecular orbital theory indicate that multi-ring chelates are formed on the cassiterite surface through chemical bonding between active stannum sites and oxygens in carboxylic and sulphonic acid groups of sulphosuccinamate.

Development of Waste Plastics-Based RDF and Its Combustion Properties

ABSTRACT The refuse-derived fuel (RDF) is manufactured using waste plastics-based materials and its physical and chemical properties are analyzed. The manufacturing process consists of hand picking, primary magnetic separation, crushing, secondary magnetic separation, feeding and extrusion. The RDF products have a high calorific values with over 6,000 kcal/kg and high stability because the waste plastics and paper are mainly used. In the present work, combustion tests with RDF products are conducted and the combustion flue gas is also analyzed to evaluate the air pollution characteristics. The combustion flue gas of RDF products is satisfied with the emission criteria of incinerator. The heavy metal concentration of combustion byproduct from the RDF boiler is also satisfied with the criteria and appears to be lower concentration than that of a common municipal waste incinerator.

Separation of Individual Plastics from Mixed Plastic Waste by Gravity Separation Processes

ABSTRACT In Korea, mixed plastic wastes generated from households after hand picking and/or mechanical sorting processes amount to 1,700,000 ton per year in 2005, and most of these waste are finally end up with landfill and/or incineration due to lacks of separation technologies and economical reasons. These plastic wastes can not be used as raw materials for chemical and/or thermal recycling because of their high content of PVC (upto 4.0 wt.%). In the present work, gravity separation system has been developed to remove PVC from the mixed plastic waste and recover the valuable plastics. The separation system mainly consists of air classification, magnetic separation, one-step crushing, feeding system at fixed rate and wet-type gravity separation system. The gravity system based on centrifugal separation has been developed and it consists of mixing, precleaning, separation, dewatering, recovery system, wastewater treatment system, etc. The main objective of this process to be developed is to achieve high separation efficiency of polyolefins (PE, PP, PS) with less than 0.3 wt.% PVC content and less than 10% moisture content in the final products. In addition, crushing unit with 8 rotor system is also developed to improve the crushing efficiency of soft-type plastics. The system with a capacity of 1.0 ton per hour is developed and operational results are presented.

Study on Recycling and Utilization of Abandoned Mine Wastes

ABSTRACT In this investigation, reprocessing tests were carried out on various types of mine wastes including metal mine tailings in order to recover valuable metallic and non-metallic resources and to minimize long-term environmental damages. Reprocessing tests on mine wastes were carried out by employing various separation techniques such as gravity and magnetic separation, classification, etc. For example, silica minerals were recovered from the coal mine wastes by applying the selective crushing and grinding, and screening methods. In the treatment of tailings obtained from metal mines, processes were also developed to recover valuable metals and non-metallic resources, which will be used for aggregates, ceramic materials, foundry sands, and other construction applications. The processes we developed should meet the major conditions such as process with large-scale treatment, easy operation and low maintenance cost, no secondary pollution problems, etc. The future prospects with regard to the utilization of raw materials recovered from the mine wastes will also be discussed.