C14 The Earth's Resources Flashcards
what are the Earth’s resources used for?
food
shelter
transport
warmth
in most cases, how are the resources that humans use produced?
agriculture
what can trees be used for?
timber
fuel
what does finite mean?
a resource that cannot be replaced as quickly as it is being used
what are some finite resources?
metals
fossil fuels
what does renewable mean?
a resource that can be replaced as quickly as it is used
what does potable water mean?
water that is safe to drink
it is low in microbes and sufficiently low levels of dissolved salts
what is pure water?
it contains just water molecules
there are no dissolved substances
how is potable water produced?
- choose a source of fresh water
- pass water through filter beds
- the water is then sterilised to kill microbes
what can be used to sterilised water?
- chlorine
- ozone
- UV light
what is desalination?
a process which reduces the levels of dissolved minerals to an acceptable level for potable water
how is desalination carried out?
- distilation
- reverse osmosis
why is desalination expensive?
both processes (distilation and reverse osmosis) require a lot of energy
what is water used for?
- drinking
- personal hygiene
- agriculture
- flushing toilets
- washing clothes
why does waste water have to be treated before going back into the environment?
it contains a large amount of organic molecules as well as harmful microbes
what are the stages of waste water treatment?
- water is screened through a mesh to remove solids
- sewage settles in sedimentation tanks which produces an effluent and sludge
- sludge is digested by anaerobic bacteria
- air is bubbled through the liquid effluent to allow aerobic bacteria to multiply
- aerobic bacteria digest organic molecules and harmful microbes
- liquid effluent is then safely discharged into rivers or the sea
what is produced in the anaerobic digestion of sludge?
biogas that is burned for electricity
what can digested sewage sludge be used for?
fertilisers for farming
what needs to be removed from water waste from industry?
harmful chemicals
what is the easiest way to produce potable water?
to use ground water from aquifers treated with chlorine
how is potable water produced when water is scarce?
directly from waste water which takes many purification steps
what does salt water need to become potable water?
it needs to be desalinated
why is copper an important metal?
it is used in electrical equipment
why do we have to extract copper from low grade ores?
the high grade copper ores are running out
how is phytomining carried out?
- plants are grown on the land containing the metal compound wanted
- the plants absorb the metal compound and concentrate it in their tissue
- plants are then harvested and burned
- the ash then contains a relatively high concentration of the metal compound
what is bioleaching?
using bacteria to extract metals
how is bioleaching carried out?
- bacteria are mixed with low grade ore
- bacteria carry out chemical reactions which produces a solution called leachate that contains the desired metal compound
what happens at the end of phytomining and bioleaching?
the desired metal needs to be extracted
this can be done with displacement or electrolysis
why is scrap iron used when extracting copper?
it is more reacive than copper and is cheap as it is scrap
what are some advantages of phytomining and bioleaching?
- they allow metals to be economically extracted from low grade ores
- they do not involve digging, transporting and disposing of large amounts of rock
what is a life cycle assessment?
carried out to assess the environmental impact of products, processes or services at different stages in their life cycle
what are the stages in an LCA?
- raw material extraction
- manufacture
- use/reuse/mainenance
- recycle/waste management
how is an LCA carried out?
- listing all energy and material inputs and outputs into the environment
- evaluate potential environmental impacts
- interpreting the results can help make decisions about using something
what is wrong with LCAs?
numerical values are assigned to the relative effects of pollutants and involves subjective judgements
what is the benefit of recycling metals?
it saves energy and the limited, finite metal ores
the pollution caused by mining and extraction is also reduced
how much energy is saved when aluminium is recycled?
95%
how much energy is saved when recycling steel?
50%
why is it difficult to recycle copper?
copper is often alloyed with other metals so has to be purified
