week 2 - inorganic contam Flashcards
what are metals
lose electrons to form positive ions (cations), great electrical and heat conductivity.
what are non metals
gain electrons to form negative ions (anions). poor conductors of heat and electricity. tend to form acidic compounds and are brittle.
what are metalloids
exhibit both metallic and non metallic behaviour
what are examples of metalloids
arsenic and antimony
what general purpose screen for inorganics contam in soil or water include what elements
vanadium, chrominium, maganese, cobalt, nickel, copper, zinc, cadmium, tin, tunteen, mercury, thalium and lead
what does a Eh-pH (ORP) diagram help indicate metal in what
metal species in solution, what happens when conditions change and solubility/stability of species
what is EC
electrical conductivity, the ability of a material to conduct electrical current, using milliSiemens per cm (mS/cm)
what is DO
dissolved oxygen, the amount of gaseous oxygen dissolved in water, measured in milligram per litre (mg/L) = ppm or percentage of saturation
when do DO concentrations decrease
higher temperature, salinity and altitude
how does temperature affect elements in water
higher temperature increases reaction rates and increase the amount of a solid that can be dissolved
what do acidic conditions help
dissolve metals and keep them in solution
what do buffers do for pH
minimise changes or raise pH
what happens when you add the buffer superphosphate fertliser
it lowers pH, mobilising metals in solution then dissolves and raises pH and metal concentrations drop
where do contaminants reside in solid phase
within crystalline materials (silicates, oxides, carbonates and sulfates)
or
sorbed to mineral surfaces
or
onto organic compounds
where do contaminants reside in liquid phase
free phase and dissolved in pore water
what are the controls on reaction rates in soil
moisture, temperature, particle size and chemical speciation
what are colloids and what do they do
particles too small to naked eye but not dissolved, metals can be transported by absorbing into them.
what conditions can increase concentration of colloids
oxidising conditions and charge colloids can attract metals and continue flowing through pore water flow.
what are sequential extractions and why is it important
5 step extraction can show whether or not total metal values might be environmentall or biologically meaningful
1. exchangeable
2. carbonates
3. organics
4. sulfates and Fe-Mn oxides
5. silicate hosted metals
what are the drawbacks of sequential extractions
expensive and no single extraction is perfect because boundaries between the reservoids overlap
what is the most widely known sequential extraction
the 5 step method
what are the two leaching tests
batch and dynamic
what are the two most relevant leaching tests in Aus
toxicity chracteristics leaching procedure (TCLP) and australian standard leaching procedure (ASLP)
metals at contaminated sites can be ? (how can they transform)
transformed into insoluble or sparingly soluble forms, their mobility and environmental risk will be reduced
what are the 6 steps to classify waste
- is material special waste
- liquid
- pre classified
- hazardous
- determing wastes classification using chemical tests
- general solid waste
how to get rid of solid waste
contaminated soil/sediment can be removed and disposed in landfills, clean fill may be implaced
what problems can arise from removing contaminated sediment/soil
oxidisation, more soluble and bioavailable
how can solid waste be contained
impermeable capping and liners, compacted clay, geosynthetic liners
how can solid waste be stabilised
macroencapsulation using cement to mix with contaminated material over 1-2 weeks keeping it moist.
what is silica microencapsulation
SME uses a metal silicate around contaminate to eliminate migration. can be used on mixed metals or hydrocarbon waste.
solid waste fixation?
orthophosphate reacts with metals to form insoluble metal phosphate salts
solid waste chemical fixation?
orthophosphate can be added as superphosphate and because its acidic, add a buffer such as magnesium carbonate. because SP is soluble it may help slow metal reactions
what is a MEP
multiple extraction procedure which simulates 1000 years of leaching
what is one method of bioremediation for solid waste
phytoextraction is the use of plants to extract and accumulate contaminants.
what is phytostabilisation
works by not taking up contaminants but stabilises the ground causing less erosion, more roughness on the surface and reducing metal solubility.
what is phytodegradation
degrades analytes as they are taken up and metabolised and can work with some organics such as pesticides, explosives, solvents and oils
microbial remediation?
works for inorganics such as cyanide. solutions readily bond to gold and silver.
how to treat water ex situ
coagulation/flocculation - additives to colloids such as aluminium sulfate reduce the negative surface charge allowing them to floc out.
settling/sedimentation - hydroclones use centrifugal accelation of water to spin grit to the side of chamber to settle and trap
what else is in the water treatment train
filtration, ultra filtration (using membranes - forming semi permeable barrier to remove materials from water), adsorption (using activated carbon) and disinfection (UV treatment and chlorination to decrease microbial activity)
what is permeable reactive barriers
a barrier with reactive filling contructed underground in the flow path of contaminated groundwater
what does the barrier media have in PRB
filters particulates and has ion exchange characteristics that allow it to remediate soil water plume. usually iron, carbon or limestone and can be mixed with sand to promote flow through
when are sequences barriers used
for mainly hydrocarbons
what reactive media used in PRB
granulated activated carbon, processed to increase surface area, granulated to keep permeability reasonable and prevent clogging of precipitates.
what is zero valent iron and when is it used
iron powder. It reduces and precipitates metals as it provides electrons (makes it negatively charged) to the contaminant for degradation. Used as ex situ water treatment
what is zero valent iron used for
soprtion of metals by reduction and precipitates metals of oxidised species
what environments help dissolve metals
acidic and oxidising environments.
what is a EC measurement used for
estimate the salt content in a sample
what are the controls on reaction rates in soil for contaminants
moisture, temperature, particle size and chemical speciation
what general screen for inorganic contaminants in soil
chromium, manganese, nickel, copper, zinc, arsenic, cadmium, mercury and lead
what general screen for inorganic contaminants in water
chromium, nickel, copper, zinc, arsenic, cadmium, mercury and lead
how can you remove exchangeables in soil/sediment
removed by deionised water rinse or acidic chelating agent
how can you extract carbonates
moderate acid such as HCI
how can you extract sulfates and Fe-Mn oxides
nitric acid or aqua regia to help break bonds because they hold metals tightly
how can you extract silicate hosted metals
need really strong acids to break down (hydrofluoric acid), but some minerals wont break down such as chromite.
what are the cons of sequential extraction
expensive, no single extraction procedure is perfect because of the boundaries between the reservoirs overlap.
why is a leachability test important
because contaminants in soil can leach into groundwater
what are water quality probes measuring
pH, ORP (Eh), EC, DO and temperature
what are the NEPM guidelines investigation and screening levels meant for
- provide the concentrations of a contaminant above which further investigation and evaluation is required
- applicably in the first stage of a site assessment
- use a CSM
- intended to help assess contam and to trigger site specific risk based approach or risk managment
what are the HIL
health investigation level:
exceeding a HIL means further investigation is required not that risk is present.
it was developed for a broad range of metals and organics in soil
its applicable for assessing human health risk
what is phytoextraction
used for solid waste such as metals and arsenic in the vadose zone by using plants to extract and accumulate contaminants. g
what is a method for inorganics such as cyanide
microbial, cyanide bonds readily bond to gold, silver etc. and commonly applied to vats or piles of crushed ore to heap leach precious metals.
gentle fertilisation and stimulation of microbes can break cyanide.
what can be used on industrial sites for ex situ water treatment
settling/sedimentation using a hydrocyclone which removes particulates by centrifugal forcing.
what are the pros to PRB
low cost, energy, maintenance, supervision, power, no dewatering and can work for years. can be <5 m long to 100s m long
what is a technique of PRB in situ for water
the fence or hanging wall where the waste at the surface contaminants groundwater and it flows through the wall to be treated.
what is a technique of PRB in situ for water
funnel and gate, which direct the flow of water towards cages that contain the reactive media (gate)
when do you use sequences barriers of PRB
with hydrocarbons where several treatments are required eg;
nutrient removal followed by reductive dissolution of chlorinated organics (using sawdust, sand to remove nitrate and then using the ZVI to dissolve trichloroethene
what are some reactive media for water treatment in situ
carbon, zeolites and organics. GAC is largely used to remove metals and organics from water
Zero valent iron (ZVI) is used to sorb metals and reductive dissolution of organics.
what is braggs law
describes the principles of XRF - The angle of the incoming radiation with respect to the crystal lattice
controls the direction and intensity of the diffracted radiation.
what is the term for disordered solids that are difficult to identify or impossible using XRF
amorphous
what is the preparation for using XRF
<10um size crystals of the sample material are grounded down using a mortar and pestle or McCrane mill
