Sedimentation

sedimentation

[‚sed·ə·mən′tā·shən] (chemistry) The settling of suspended particles within a liquid under the action of gravity or a centrifuge. (geology) The act or process of accumulating sediment in layers. The process of deposition of sediment. (metallurgy) Classification of metal powders by the rate of settling in a fluid.

Sedimentation

The natural process of depositing sediment.

Sedimentation

the settling or surfacing of particles in the dispersed phase, such as solid particles, liquid droplets, or gas bubbles, in a liquid or gaseous dispersion medium as a result of a gravitational field or centrifugal force. Sedimentation occurs if the directional motion of the particles under the effect of gravity or centrifugal force predominates over the random thermal motion (seeBROWNIAN MOVEMENT and DIFFUSION).

The rate of sedimentation depends on the mass, size, and shape of the particles, the viscosity and density of the medium, and the acceleration caused by the force field. For fine spherical partices that do not interact with each other, the sedimentation rate can be determined by Stokes’ law. Sedimentation in dispersed systems—especially in a gaseous dispersed medium—is often accompanied by an increase in the size of the settling particles as a result of coagulation or coalescence.

Sedimentation in nature causes the formation of sedimentary rocks, the clarification of water in large bodies, and the release of liquid drops and solid particles from the atmosphere.

In industry, sedimentation is used in the separation of powders into fractions and the isolation of various products in chemical engineering. (See alsoELUTRIATION and SETTLING.)

Sedimentation (industry)

The separation of a dilute suspension of solid particles into a supernatant liquid and a concentrated slurry. If the purpose of the process is to concentrate the solids, it is termed thickening; and if the goal is the removal of the solid particles to produce clear liquid, it is called clarification. Thickening is the common operation for separating fine solids from slurries. Examples are magnesia, alumina red mud, copper middlings and concentrates, china clay (kaolin), coal tailings, phosphate slimes, and pulp-mill and other industrial wastes. Clarification is prominent in the treatment of municipal water supplies.

The driving force for separation is the difference in density between the solid and the liquid. Ordinarily, sedimentation is effected by the force of gravity, and the liquid is water or an aqueous solution. For a given density difference, the solid settling process proceeds more rapidly for larger-sized particles. For fine particles or small density differences, gravity settling may be too slow to be practical; then centrifugal force rather than gravity can be used. Further, when centrifugal force is inadequate, the more positive method of filtration may be employed. All those methods of separating solids and liquids belong to the generic group of mechanical separations. See Centrifugation, Clarification, Filtration

Particles too minute to settle at practical rates may form flocs by the addition of agents such as sodium silicate, alum, lime, and alumina. Because the agglomerated particles act like a single large particle, they settle at a feasible rate and leave a clear liquid behind.

sedimentation

rate

[rāt] the speed or frequency with which an event or circumstance occurs per unit of time, population, or other standard of comparison.adjusted rate a fictitious summary rate statistically adjusted to remove the effect of a variable, such as age or sex, to permit unbiased comparison between groups having different compositions with respect to these variables. See also rate" >crude rate and rate" >specific rate.attack rate in the analysis of acute outbreaks of disease, the proportion of persons who are exposed to the disease during the outbreak who do become ill.basal metabolic rate an expression of the rate at which oxygen is utilized in a fasting subject at complete rest as a percentage of a value established as normal for such a subject. Abbreviated BMR.birth rate the number of live births in a geographic area in a defined period, usually one year, relative to some specified population. For the crude birth rate, it is the average total population or the midyear population in the area during the period. Specific birth rates for subsets of the population may also be calculated, for example, an age-specific birth rate is limited to the population of females of a defined age range.case fatality rate the number of deaths due to a specific disease as compared to the total number of cases of the disease.crude rate one giving the total number of events occurring in an entire population over a period of time, without reference to any of the individuals or subgroups within the population. See also rate" >adjusted rate and rate" >specific rate.death rate the number of deaths in a certain period of time divided by the total of a given population. The crude death rate is the ratio of the number of deaths in a geographic area in one year divided by the average population in the area during the year. The age-specific death rate is the ratio of the number of deaths occurring in a specified age group to the average population of that group. The cause-specific death rate is the ratio of the number of deaths due to a specified cause to the average total population. Called also mortality rate.

Historic example of death rates (per 100,000) for leading causes of death for men aged 25–44 years. From Centers for Disease Control and Prevention: Morbidity and Mortality Weekly Report 42:483, 1993.DEF rate an expression of dental caries experienced in primary teeth, calculated by adding number of those requiring filling (D), decayed teeth requiring extraction (E), and those that have already been successfully filled (F); missing primary teeth are not included in the calculation.DMF rate an expression of the condition of the permanent teeth based on the number of teeth decayed, missing (or indicated for removal), and filled or bearing restorations. It is calculated by adding the number of carious permanent teeth requiring filling (D), carious ones requiring extraction (Mr), ones previously extracted because of caries (Mp), and permanent teeth (F).dose rate the amount of any therapeutic agent administered per unit of time.erythrocyte sedimentation rate (ESR) see erythrocyte sedimentation rate.fatality rate the rate" >death rate in a specific group of persons simultaneously affected by some event or circumstances, such as a natural disaster.fertility rate a measure of fertility in a defined population over a specified period of time, usually one year; particularly the rate" >general fertility rate, but also including more specific rates such as those for females of a given parity or a particular age range or that describing the completed rate for females who have finished childbearing.fetal death rate the ratio of the number of fetal deaths in one year to the total number of both live births and fetal deaths in that year.five-year survival rate an expression of the number of survivors with no trace of a given disease five years after each has been diagnosed or treated for the disease.flow rate flow (def. 2).forced expiratory flow rate forced expiratory flow.general fertility rate the most widely used measure of fertility; the number of live births in a geographic area in a year per 1000 women of childbearing age, which is usually defined as age 15 to 44 years.glomerular filtration rate an expression of the quantity of glomerular filtrate formed each minute in the nephrons of both kidneys, calculated by measuring the clearance of specific substances, e.g., inulin or creatinine.growth rate an expression of the increase in size of an organic object per unit of time.heart rate the number of contractions of the cardiac ventricles per unit of time (usually per minute).incidence rate the risk of developing a particular disease during a given period of time; the numerator of the rate is the number of new cases during the specified time period and the denominator is the population at risk during the period. Compare prevalence r.infant mortality rate the ratio of the number of deaths in one year of children less than one year of age to the number of live births in that year.intrinsic rate in pacing" >cardiac pacing terminology, the heart rate unaided by an pacemaker" >artificial pacemaker, expressed in beats per minute (bpm). See also length" >cycle length.maternal mortality rate a rate in which the numerator is the number of maternal deaths ascribed to puerperal causes in one year; the number of live births in that year is often used as the denominator, although to make a true rate the denominator should be the number of pregnancies (live births plus fetal deaths). Called also puerperal mortality rate.maximal expiratory flow rate (MEFR) maximal expiratory flow.maximal midexpiratory flow rate (MMFR) maximal midexpiratory flow.mendelian rate an expression of the numerical relations of the occurrence of distinctly contrasted mendelian characteristics in succeeding generations of hybrid offspring.metabolic rate an expression of the amount of oxygen consumed by the body cells.morbidity rate an inexact term that can mean either the rate" >incidence rate or the rate" >prevalence rate.mortality rate death rate.neonatal mortality rate the ratio of the number of deaths in one year of children less than 28 days of age to the number of live births in that year.paced rate in pacing" >cardiac pacing terminology, the rate of pulses of an pacemaker" >artificial pacemaker, expressed as pulses per minute (ppm). See also length" >cycle length.perinatal mortality rate the ratio of the number of the sum of fetal deaths after 28 or more weeks of gestation (stillbirths) and deaths of infants less than 7 days of age in one time period and population to the sum of the number of live births and fetal deaths after 28 or more weeks of gestation (stillbirths) in that same time period and population.postneonatal mortality rate the ratio of the number of deaths in a given year of children between the 28th day of life and the first birthday relative to the difference between the number of the live births and neonatal deaths in that year; the denominator is sometimes simplified, less correctly, to the number of live births. The ratio is sometimes approximated as the difference between the infant mortality rate and the neonatal mortality rate.prevalence rate the number of people in a population who have a disease at a given time; the numerator is the number of existing cases of disease at a specified time and the denominator is the total population. Time may be a point or a defined interval, and is traditionally the former if unspecified. Compare incidence r.puerperal mortality rate maternal mortality r.pulse rate the rate of the pulse, measured as number of pulsations in an artery per unit of time; normally between 60 and 80 per minute in an adult.respiration rate the number of inhalations and exhalations per unit of time, usually measured by observation of chest movements and averaging 16 to 20 per minute in an adult.sedimentation rate the rate at which a sediment is deposited in a given volume of solution, especially when subjected to the action of a centrifuge; see also erythrocyte sedimentation rate.slew rate in pacing" >cardiac pacing, the rate, expressed in units of mV/msec, at which an R wave reaches peak amplitude; it represents the maximum rate of change of amplifier output voltage.specific rate a rate that applies to a specific demographic subgroup, e.g., individuals of a specific age, sex, or race, giving the total number of events in relation only to that subgroup. See also rate" >adjusted rate and rate" >crude rate.stillbirth rate fetal death rate.

sed·i·men·ta·tion

(sed'i-men-tā'shŭn), Formation of a sediment.

sed·i·men·ta·tion

(sed'i-mĕn-tā'shŭn) Formation of a sediment.

sedimentation

sed·i·men·ta·tion

sedimentation

sed•i•men•ta•tion

Sedimentation

sedimentation

Sedimentation

Sedimentation

Sedimentation (industry)

sedimentation

rate

sed·i·men·ta·tion

sed·i·men·ta·tion

sedimentation

Synonyms for sedimentation

noun the phenomenon of sediment or gravel accumulating

Synonyms

Related Words