CARBON FOOTPRINTThe total amount of green house gasproduced to directly and indirectly supporthuman activities , usually expressed inequivalent tons of carbon dioxide (CO2).
GLOBAL WARMING POTENTIALGlobal-warming potential (GWP) is a relativemeasure of how much heat a greenhouse gas traps inthe atmosphere.For example, the 20 year GWP of methane is 72, which meansthat if the same mass of methane and carbon dioxide wereintroduced into the atmosphere, that methane will trap 72 timesmore heat than the carbon dioxide over the next 20 years
SCRAP METAL RECYCLE• Pressing• Crushing• Shearing• Sorting• Smelting
The biggest savings are with aluminium where the recycled only takes 6%of the energy, but other pollution is caused in the production both times.12kg of CO2 are produced per kg aluminium from bauxite but only 1.7 kg CO2from recycled aluminium. PollutionCarbon FootprintKgs of CO2 produced per kg of metalAluminium from bauxite 12Aluminium recycled 1.7Brass from ores 6.7Brass recycled 1.7Carbon FootprintSteel from ore 2.82Steel recycled 0.5Carbon FootprintKgs of CO2 produced per kg of metalCopper from ore 5.5Copper recycled 1.4-4Carbon FootprintAluminium has the highest CO2 production per kg but it is much lighter thanmost metals.
BiohydrometallurgyBiohydrometallurgy can be defined as the field of applications resulting fromthe control of natural (biochemical) processes of interactions betweenmicrobes and minerals to recover valuable metals. It is a subfield within hydrometallurgy which includes aspects of biotechnology. It is used to perform processes involving metals, for example, microbial mining, oil recovery, bioleaching, water-treatment and others. It is mainly used to recover certain metals from sulfide ores. It is usually utilized when conventional mining procedures are too expensive or ineffective in recovering a metal such as copper, gold, lead, nickel and zinc.
BIOLEACHINGBioleaching is the extraction of metals from their ores through the use of livingorganisms. This is much cleaner than the traditional heap leaching usingcyanide.Bioleaching is used to recover copper, zinc, lead, arsenic, antimony,nickel, molybdenum, gold, silver, and cobalt.Bioleaching techniquesRole of microorganisms in mineral bio-oxidation:• Microbes produce the leaching chemicals.• Microbes also provide the most efficient reaction space for bioleaching to occur
Cu2+(aq) + 2LH(organic) → CuL2(organic) + 2H+(aq) Because this complex has no charge, it is no longer attracted to polar watermolecules and dissolves in the kerosene, which is then easily separated fromthe solutionCu2+(aq) + Fe(s) → Cu(s) + Fe2+(aq)
The bacterium Paenibacillus polymyxagrown in the presence of hematite.
BENEFITS OF BIOLEACHING• Simple and inexpensive process. Substantially lower capex and opex than in traditional smelting and refining processes• No sulfur dioxide emissions as in smelters.• No need for high pressure or temperature• Leaching residues less active than in physico-chemical processes• Ideal for low grade sulfide ores – lower cut-off rate possible
Nanoscavengers - a simple approach to metal extraction SEM image of the HOC18-nanoscavenger This method, termed the nanoscavenger concept, is based on silica particles and is an easy, green approach to the collection and concentration of metals for analysis. The technique is expected to yield both environmental and cost benefits. Analytical chemists regularly need to remove metals from aqueous solutions so they can be analysed. Extraction into organic solvents is currently the most popular procedure for doing this. Howard and Khdarys approach uses chelating organic ligands to modify the surface of silica spheres with an approximate diameter of 250 nm. These particles are able to bind to metals temporarily, and can be collected easily from solutions.
The concept behind this research is beautifully simple. The nanoscavenger movesnaturally through the solution under examination, binding any metal with which itcomes into contact. This movement, using Brownian motion, means that no physicalagitation is required. Simple filtration removes the metal-bound nanoscavengerfrom the solution. Finally, separation of the metal and nanoscavenger allowsanalysis of the metal using standard detection methods.A wide range of organic materials can be extracted on the surface ofnanoscavengers by hydrophobic interaction. This is can be achieved by modifying ofthe silica surface with different organic groups. Indeed, large particle size modifiedsilica has been widely and successfully used for the pre-concentration of drugs andpesticides.
ADVANTAGES OF NANOSCAVENGING TECHNIQUE the technique is environmentally friendly as smaller volumes of organic solvents are used than with the other extraction methods and only small quantities of nanoscavenger (50-200 mg) need to be dispersed. Large numbers of samples can be quickly and simultaneously treated, even at the sampling site. One of the most important physical advantages of this procedure is less human or mechanical effort is needed as no mechanical agitation is required.