CA1165513A - Preparation and expansion of perlite ore fines - Google Patents
Preparation and expansion of perlite ore finesInfo
- Publication number
- CA1165513A CA1165513A CA000382050A CA382050A CA1165513A CA 1165513 A CA1165513 A CA 1165513A CA 000382050 A CA000382050 A CA 000382050A CA 382050 A CA382050 A CA 382050A CA 1165513 A CA1165513 A CA 1165513A
- Authority
- CA
- Canada
- Prior art keywords
- perlite
- perlite ore
- ore fines
- fines
- temperature
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B14/00—Use of inorganic materials as fillers, e.g. pigments, for mortars, concrete or artificial stone; Treatment of inorganic materials specially adapted to enhance their filling properties in mortars, concrete or artificial stone
- C04B14/02—Granular materials, e.g. microballoons
- C04B14/04—Silica-rich materials; Silicates
- C04B14/14—Minerals of vulcanic origin
- C04B14/18—Perlite
Abstract
Abstract of the Disclosure A process is described for the preparation of perlite ore fines for expansion. The ore fines are treated with an agglomerating agent which has a viscous liquid phase at a temperature above ambient temperature but below the critical dehydration temperature of the perlite ore fines. Suitable agglomerating agents mentioned are the boron acids, particularly orthoboric acid and metaboric acid. The perlite ore fines and agglomerating agent are mixed, preferably by mixing, and then heated to the temperature of the viscous liquid phase and held at that temperature for a short period while the liquid coats at least a portion of the perlite ore fines and effects agglomeration.
Thereafter, the agglomerated perlite ore fines can be expanded in a conventional perlite ore expander. The resulting expanded materials have properties essentially identical to standard expanded perlite ore and are useful for such purposes as insulating fillers and light weight aggregates.
Thereafter, the agglomerated perlite ore fines can be expanded in a conventional perlite ore expander. The resulting expanded materials have properties essentially identical to standard expanded perlite ore and are useful for such purposes as insulating fillers and light weight aggregates.
Description
PREPARATION ~D EXPANSION OF PE~LIrE ORE FIN~S
~echnicaL_~igl~
me invention here relates to the processing of perlite ore.
More particularly, it relates to a method for converting perlite ore fines into expanded perlite.
Back~ound of Prior Art Perlite is a mineral of volcanic oric~in which generally falls into the rhyolitic class. A unique feature of perlite is that it contains several percent of bound waterO If perlite ore is rapidly heated to a temperature on the order of 1600F (870~C~, the water is converted to steam and the perlite "pops", i.e., it expands rapidly to a much lower density. me amount of expansion is usually on the order of 4 to 20 times the original volume and the final density of the expanded perlite granules will normally be in the range of about 3.5 to lbs/ft3 (0006 to 0.08 g/crn3) for use as insulating fillers or about 7 to 15 lbs/ft3 ~0.11 to 0.24 g/cm3) for plaster aggregate use. (The exact mechanism of the water-induced expansion is quite complex; see Lehmann et al, "m ermoanalytic Research on Perlite and Perlite-Type R~cks," ~DJn~.=Z5g., volO 100, no~ 7, pp 271 274 (1976). For the purposes of ~he invention herein, however, the above simplified description of the expansion is entirely adequate.) Perlite ore is normally expanded in large vertical chambers known as "expanders". At the bottom of each expander is a flame generating burner. The perlite ore to be expanded is dropped into the expander at a point above the flame and drops through the hot zone created by the flame. In this hot zone, the perlite particles expand and, because of their expanded volume, are then turned around and carried out of the top of the expansion chamber entrained in the exhaust gas stream. Operation of a typical perlite expander is shown in U.S. Patent No. 2,572,484 with another variation shown in U.S.
Patent No. ~,639,132.
It has been found over the years that the perlite ore, in order to be expanded satisfactorilyr must be in the form of particles or granules having a si~e of from about +2QO mesh (greater than 74 um) ~ ~ 6~S~3 up to approximately 3 to 4 mesh (approximately ~ inch or 6 mm). Larger partid es do not expand well because their weight pulls them through the flame zone too quickly for them to be heated to the expansion temperature and in addition their greater size and stronger structure prevents heat from penetrating to the center of the particle to convert the water to steam and also prevents the steam irom f~ly "popping" the large rigid particle. The presence of these larger particles in the perlite ore prior to e~panding causes no significant problems to the perlite ore processor, for such larger materials can be readily screened out of the raw material ore stream from the expanders and recycled to crushing or other size reduction equipment to reduce the large granules to the optimum size for expansion.
At the other end o the size scale, however, the material known as "ore fines" which have particle sizes not greater than 200 mesh (not greater than 74 um) do pose a significant problem for ~he ore processor. These materials do not expand well because their light weight and small size causes them to be entrained in the exiting air and gas stream in an expander before they have dropped far enough to encounter the appropriate temperature for expansion. In addition, such fine materials do not move well through the ore handling systems normally in use, which commonly rely in part on gravity feed.
Consequently, in the past, ore producers have considered the ore fines to be essentially waste material, although to some extent such unexpanded fine materials may find uses. Generally, however, since the largest market for perlite products is for expanded perlites, the ore processor is desirous of expanding as much of the ore raw material as possible~
It would be possible to handle such fine material if the individual fine particles were agglomerated into larger units which fall in the particle size range for conventional perlite eXpQnSiOn.
However, heretofore the known processes for agglomerating "perlite fines" have been processes intended to be used with previously expanded material. In the process of expansion, perlite (which is a somewhat brittle material) often shatters upon expansion leaving a substantial amount of fragments of expanded perlite. These fragments are themselves frequently referred to as "fines" but it must be ~mderstood that these are "expanded fines" as contrasted to the "ore fines" which :~3 5 ~ 3 are unexpanded and which are the subject of the present invention~
U~S. Patents Nos. 3~23S,635 and 4,175,158 both describe processes for agglomerating the expanded perlite fines by addition of water, a fluxing agent or, in the case of ~.S. Patent No. 4,175,158, boric acid. An integral part of both of these described processes, however, is heating and maintaining the expanded perlite fines at temperatures on the order of about 1200 to 1700F (650 to 925C). At these temperatures, the fluxing materials such as soda ash or B2O3 (from the boric oxide) act to fuse the expanded perlite fines into larger granules. Such processes are not applicable to ore fines of perlite, hcwever, because exposing the perlite ore to such temperatures will either cause the perlite to pop (if the exposure to the temperature is rapid) or will cause the water of hydration to slowly vaporize and be removed from the ore particle (if the perlite is slowly raised to that temperature) thus leaving no water of hydration to cause the perlite subsequently to pop.
It would therefore be highly desirable to have a process whereby the fine material in perlite ore raw materials can be agglomerated at relatively low temperatures to produce a particle of the appropriate size for conventional expansion.
Brief Summary of_the Invention The invention herein is a process for preparing perlite ore fines for expansion which comprises mixing the perlite ore fines with an agglomerating agent, the ~gglomerating agent having a viscous liquid phase at a temperature above room temperature but below the critical dehydration temperature of the perlite ore fines with the viscous liquid phase being capable of at least partially coating the perlite ore fines. m ereafter, the perlite ore fines are agglomerated by heating the mixture of the fines and the agglomerating agent to a temperature at which the agglomerating agent exists in the viscous liquid phase and maintaining the temperature for a period of time sufficient to obtain agglomeration of the fines by the agglomerating ayent.
In another aspect, the invention comprises preparing the perlite ore fines for expansion as described above followed by rapid heating of the prepared perlite ore fines to a temperature at which the perlite ore fines expand.
i J65513 ~ e pr~-fe~red ayglo~erating c~ents ~re n~aterials o the koron acid s~stem.
Detailed ~escrip-tion of ~h~ In-~entlon The pres~nt i~ven~ion involves ~he treating of perlite ore fines to r~3Xe th~ suitable for e~ ~nsion Ln a ~nvention~l perllte eYpander. The "ine" portion of -the Ferlite ore, as detel~Lned after the ore ras been oonventionally cleaned, crushed, screened and ~therwise made ready for expansion, is normLally defined as that portion of the ore which exists as particles having particle siæes of not greater -t~an 2C0 mesh (i.e., not greater than 7~ ~n). It will be understo~d, however, that there i5 no absolute and distinct dividlng line betwe,~n ~terials cons~dered "fines" and larger Ferlite particles considered to be conventional e.~,~indible p_rl~te. Thus, ~hile perlite havir,g particle sizes of not greater than 7~ um ( 200 mesh) is qenerally considered to constitute perlite ore fines, in some circumstances particles ~hi^h are larger than 74 um can also be considerea t~ be "fine". For instance, in mos~ conventional particle size sep2~a.or devices, there is not a sharp cut-off of particles at a s,pecifi0d si~e. ~ather -there is a distri~ution of particle sizes wit`n the princlpal seg~ent ~ing of t~e designated size but with ~e enti, e mass of s2plrat~d Ea~rticles ~lso containing scme material of larger and/or smaller size. Su~h i5 the case with ccmmercial perlite ore separation, ~here ~he "ore fines" fraction rlormally contains a portion havi~ E~u~ticle sizes above 74 um. m erefore, Sor the ~urposes of ~his invention, ~he "ore fines" wllich are beneficially agglc~nerated by the process o~ ~is invention will ~e definc~d as a nuLYture of perlite particles at least 50%, and preferably at least 70%, of whic~h have ExLrticle sizes of not greater than 74 um.
After ~he perlite ore fines (as defined a~ove) have been separated frGm the rem~inder of ~he perlite ore follcwm g conventional ~uning, drying, c~ shing, sizirlg and okher processes utili~ed in t~,e perlite ore produc-tion industry to prepare raw ma~erials for exFx~si~n, the fines are treatc~d in accordance with the present invention. They ar~ ~irst ~uLxed with a suitablr agglcmerating agent having t~e properties ~o be descri~ed ~elc~. Conveniently such agglcme..atillg agent is a colid material a~ amblent temperatures and mcst conveniently, the agglcme-rating agent has been ccmninuted into sQlid ~ ~65513 ~5--particles of approximately the sc~me particle size as the perlite ore fines. The perlite ore fines and agglomerating agent are blended and dry mixed by conventional mixing means such as rib~on blenders to form preferably a dry mixture of fines and agglomerating agent. Where the agglomerating asent is a liquid or has a liquid com~onent at ambient conditions, it is desirable to mix the fines and agglomerating agent and then dry the mixture to facilitate subsequent handling of the mixture.
The agglomerating agent will be a material which is compatible with perlite and which has a viscous liquid phase at ~
temperature above ambient temperature but below the dehydration temperature of the perlite. The viscous liquid phase must be one that will effect at least partial coating of the perlite ore fines with the liquid. Materials which have such liquid phases at the indicated temEeratures but which do not also effect such coating are not suitable for use in the present invention. Examples of such materials which have been tried but fo~nd not to work are hydrated sodi~n silicate and hydrated sodium carbonate ("soda ash"). The preferred materials which do mleet the required conditions are materials of the boron acid system, notably orthoboric acid (H3BQ3) and metaboric acid (HBO2).
Orthoboric acid is a colorless or white powder at ambient temperatures with a specific gravity of 1.43. At a temperature of approximately 340F (170C), orthoboric acid is transformed to metaboric acid.
Metaboric acid is a white crystalline solid at ambient temperatures 25 with a specific gravity of approximately 2.49. At approximately 460~F
(236C), the metaboric acid melts, forming a viscous liquid which may contain some crystals and which recrystallizes upon cooling. The phase change of metaboric acid from solid to liquicl at the melting point also results in approximately a 10-fold increase in the surface area. This liquid readily coats onto the perlite ore fine particles.
Descriptions of the boron acid system and the viscous metaboric acid liquid can be found in Kracek et al, "m e System, Water-Boron Oxide," er~ J~ Q~ Sci~, vol 35-A, pp. 143-171 (1938~; in De Bore (ed.), gs~s~,ie~ 5~ (1961) in the section by Dollimore et al, "m e Kinetics of the Thermal Decomposition of ~ome Substances Which Decompose to Oxides, and the Production of Active Solids by Such Processes" pp. 627-637; in Kemp, ~ t~ y~L~t~ B
~f' l 3 (1956), pp. 9-21; and in Kirk-Othmer (eds.), ~bçyclgeç~ f Cpemica Technology (3rd ednO, 1978), Vol. 4, pp~ 67-77.
rme agglomerating agent ~y be present in any amount from Q~1% to about 10% b~ weight based on the weight of the perlite ore fines, with the agent preferably being present as from 0.5 to 3 weight percent.
Following mixing of the perlite ore fines and the agglomerating agent, the blended materials are subjected to heating to a temperature at which the agglomerating agent is converted to the viscous liquid phase, but which temperature does not exceed the "critical dehydration temperature" of the perlite. For the purposes of this invention, the term "critical dehydration temperature" in fact represents time-temperature combinations. It is known that the ability of perlite to expand is based generally on essentially all of the bound water being simultaneously con~erted to steam, so that the expansion of the water on vaporization causes the perlite to expand as it seeks to escape from the particle. If, however, the bound water is vaporized slowly, each increment of vc~porized water will have time to diffuse or migrate slowly out of the unexpanded particle, ultimately leaving the perlite particle so depleted of water that rapid heating of the particle under normal expansion conditions will not result in expansion. m is slow "dehydration" of the particle ~which is "slaw" in comparison to the rate of the normal expansion-causing vaporiza'ion~
occurs at varying rates which are dependent on both the temperature to which the perlite is expo æd and also to the length of time of that exposure. As the temperature rises, the period of exposure time necessary to effect sufficient dehydration to prevent expansion is decreased. (At a sufficiently high temperaturer of course, vaporization occurs so rapidl~ and so uniformly across the particle that e~pansion is induced, since there is not sufficient time available to let the vaporized water escape from the particle by migration and/or diffusion~) In generalr at temperatures below about 1000F (540C), and especially below about 700F (370C), significant dehydration does not occur in the time periods required for the liquification and application of the agglom~rating agent. m erefore the effect of time can be simplified b~ merely requiring that the liquification and application of the agglomerating agent be conducted at a temFerature . 3 below the "critical deh~dration temperature," i.e., that temperature at which the time period of the liquification and application would be the minimum tLme in which significant dehydration could occur.
Normally the dry mixing and heating are done in separate but closely sequential steps. They could, however, be performed simultaneously by using a heated mixer. Alternatively, if the agglomerating agent is a stable material, mixing could take place long beEore heating with the mixed material simply being stored until time to be heated. m is would also permit the mixing and heating to be conducted at separate locations which are perhaps even quite remote from each other.
Tha time of maintenance at temperature is dependent upon the particular agglomerating agent being used. For the boron acids, it has been found that a time of 4 minutes at 600F (315C) provides quite satisfactory agglomeration of perlite fines. m e heating time should bé kept as short as possible commensurate with good agglomeration because of the tendency of the perlite to dehydrate over prolonged heating periods, even at relatively low temperatures. Heating times on the order of 1 to 20 minutes, preferably 3 to 10 minutes, are considered to be quite adequate.
In one aspect of the invention, the perlite ore fines ~hich have completed their heating with the agglomerating agent are passed directly to a perlite expander where they are expanded. This is quite feasible when the expander has associated therewith a pre-heat chamber into which the mixed perlite and agglomerating agent can be placed for heatin~. m e pre-heat chamber discharges into the expander feed system so that the agglomerated perlite ore fines can be fed directly to the expander for expansion. ~lternatively, however, the agglomerating agent will be one which can be cooled and then rapidly re-melted during expansion. mis would permit the perlite ore processor to agglomerate the ore fines with the agglomerating agent at the mine, mill or other ore producing or preparation site, then store or ship the agglomerated perlite ore fines to a remote location for exFansion with the agglomerated fines being put directly into the expander feed system without any further heating. This is the preferred manner of handling the heat treating and expansion. This is due to several factors: 1) Many perlite expanders are of rather small capacity and do not have .
S S ~ 3 heating equipment available in conjunction with the expander.
Consequently the processor wishing to use this proces~ in conjunction with perlite expansion would frequently be forced to add a heating unit at considerable cost to his perlite expansion equipment 2) Cnce the boric acid is coated on the perlike particles, the two components will not segregate as they would if they were merely blended into a simple dry mixtureO 3) A more uniform agglomerated fines product can be obtained, since the ore producer treats the perlite ore fines and thus can run a single consistent operation, rather than having a number of different end users treating perlite or fines in a variety of different types of mixers, heaters and under perhaps significantly different conditions. Such cooling, re-heating and remelting are quite feasible when orthoboric acid is used as the agg]omerating agent.
Once the perlite ore fines have been agglomerated with the agglomerating agent and heated for the appropriate time~ they are then ready to ~e expanded in a conventional perlite expander. As noted above, the expansion can come immediately after the heat treating or it can be delayed for any desired length of time. Expansion of the treated perlite ore fines is in the same manner as conventional perlite expansion of the larger normal perlite particles. me perlite ore fines can be expanded by themselves or can be mixed into a common feed with the original standard size perlite feed particles.
me examples below will illustrate the process of this invention. In these experiments, both the standard perlite ore materials and the perlite ore fines were from a commercial New Mexico perlite mining ~peration. Conventional mining, cleaning, crushing, sizing and other ore processing techniques were used. Agglomeration was with orthoboric acid in amounts of 1 or 2 percent by weight of the perlite ore fines, as noted. The fines portion of the ore was defined to be that portion in which 70~ of the particles were of 74 um particle size or smaller. ~eating of the ore fines/agglomerating agent mixture was for 4 minutes at 600F (315C). The 'ISeries A" runs illustrate the expansion of the perlite to the lowest achievable loose weight "Series B" are experiments in which the perlite was expanded to a loose weight in the range of 3 to 4 lb/ft3 (0.048 to 0.064 g/cm3), which is the conventional density for perlite use as an insulating filler~ The processing conditions were otherwise the same as in "Series A". "Loose 5 5 ~ 3 _g_ weight" is often referred to as l'bulk density" or "apparent densi~y"
and refers to the nominal density of a loosely packed powder.
T~ble 1 below shows the particle s,ize distributions o~ the pexlite ore fines and the standard ore as well as various expanded materials.
3 5 5 :1 3 o oO o ~ o~ ~ o ca C
a~ ~ 0~ o o o o~ ~ o w o ~ .~ o U C) ~ ~ r r ~ r ~ r~l r~
C
P~ Ed ~ ~Q
~ ~ ,~ r~ r~
~ 4 a) ~ a ~ ~ In O ~D O ~ -1 0 S_l r ~ ~ r_l r--l r~l ~ ~ r~ r~l dl ~, I¢ (~
V L l .r ~1 a~ O ~ ~ u~
S~.y O G~ a:~ ~ It'~ ~ ~ r-l i 1~
- . r ~ 3 - O
c 8 ~ ~ ~ o o o o u~
1~ L cn rl ~ D O
Ul~
~rC ' r q~ ~ ~5 ~ -1 0 CO u~ 1 h ~
O C ~
o o ~r o o o o o o o o ~ ~rl ~ ~ ~o o In æ ~ ~
~3 -10-.
~ ~S513 Table 2 below illustrates typical properties of the expanded materials. The "energy consumption" is the amount of energy required to expand the indicated material.
T~LE 2: _ S~RIE,S A
Loo~e_WQcLD~t Energy 3 3 ReCovery~ 5~i~ymE~iQ~aL
lb~f~ ~ç~_ ~ B~lb Non-agglomerated 2.1 0~034 83~3 23000 12800 Ore Fines Agglomerated 1O8 0.029 90.0 9940 5520 Fines (1%
boric acid) Agglomerated 1.67 0.027 94.5 13600 7560 Fines (2%
boric acid) Standard 1.62 0.026 92.9 18300 10200 Ore Note: (a) The data here are for a small (laboratory scale) expander.
The relative energy consumption per unit of perlite weight would be expected to be 8-10 times less for a commercial scale expander.
It will be evident from these experimental clata that the agglomerated perlite or fines expand to a size and loose weight essentially equivalent to that of standard perlite ore.
Similar data are presented in Tables 3 and 4 below for the "Series B" materials.
.
~ ~ O O C:~ ~ ~ ~ ~I ~ ~ ~ ~
c~ ~
r~
a ~ ~ a ~ o $a) u ~ tl) r~
l r ~ EL
rc ~3 r~
~ ~ ~ o OD ~r o r~ 1 o ~ C) r~
r ~ 3 ~:
CY L l ~r~
U~ (~ IL~ ~i ~_ a~ ~ o u~ 0 ~ ~ ~ ~1 1 0 4~
r ~ ~: r-l o a ~
~ aJ
c o a ~d . ~ ~ '` 0 o o ~
C40' I
,- rcl .
~ ~ a~ o co u~ I I r-l ~i rc~ -.a ~a ~ d ~ o o ~r o o o o o o o o ~ r~
~ a ~ u~ r~ o u~ o o o o ~ o . 1~ a~ ~
Ll l!~ r-l r-l ~ t~ ~ I N JJ
~u ~u~ æ
~3 -12-~yL~-9~ ERIEs B
__~Q~ Weight Energy 3 Recovery, Consume~ion~aL
~ t ~ _ % ~ Cal~
Non-agglomerated 3.5 U.056 89.1 15800 8740 Ore Fines Agglomerated 3.0 0.048 92.4 9080 5040 Fines (1%
boric acid) Agglomerated 3.5 0.056 94.4 7670 ~260 Fines (2%
boric acid) Standard 3~72 0.059 93.6 16200 9000 Ore Note: ~a) m e data here are for a small ~laboratory scalel expander.
The relative energy consumption per unit of perlite weight would be expected to be 8-10 times less for a commercial scale expander.
It will be evident Erom these data that the agglomerated fines of the process of this invention following expansion are equivalent to standard expanded perlite ore used for insulating fillers. In addition, the data from both Series A and Series B
indicate that the eneryy input required to expand the agglomerated fines is significantly less than that required to expand standard perlite ore. In addition, both the Series A and Series B experiments clearly indicate that the agglomerated perlite fines yield significantly greater recovery and significantly higher median particle si~es than the expanded perlite ore fines without any agglomeration.
The latter property is particularly significant since the value of an expanded perlite as an insulating or cement filler is directly proportional to the particle size of the perlite.
~:16~3 1~--e~
m e invention herein relates to ~he perlite expansion industry. It is particularly useful in the expansion of the fine portion of perlite ore~ Expanded perlite ores find utility as thermal insulations in such materials as structural roofing boards and insulating wall boards for residential, commercial and industrial buildings. Expanded perlite also finds considerable use as a light weight aggregate for construction materials such as plaster, gypsum and concrete. Construction panels made of the materials containing light weight aggregates are used where strength is not a prime requirement but where fire resi~tance, insulation and light weiyht are major considerations. Typical applications include instalJation in tall buildings and long span bridges.
~echnicaL_~igl~
me invention here relates to the processing of perlite ore.
More particularly, it relates to a method for converting perlite ore fines into expanded perlite.
Back~ound of Prior Art Perlite is a mineral of volcanic oric~in which generally falls into the rhyolitic class. A unique feature of perlite is that it contains several percent of bound waterO If perlite ore is rapidly heated to a temperature on the order of 1600F (870~C~, the water is converted to steam and the perlite "pops", i.e., it expands rapidly to a much lower density. me amount of expansion is usually on the order of 4 to 20 times the original volume and the final density of the expanded perlite granules will normally be in the range of about 3.5 to lbs/ft3 (0006 to 0.08 g/crn3) for use as insulating fillers or about 7 to 15 lbs/ft3 ~0.11 to 0.24 g/cm3) for plaster aggregate use. (The exact mechanism of the water-induced expansion is quite complex; see Lehmann et al, "m ermoanalytic Research on Perlite and Perlite-Type R~cks," ~DJn~.=Z5g., volO 100, no~ 7, pp 271 274 (1976). For the purposes of ~he invention herein, however, the above simplified description of the expansion is entirely adequate.) Perlite ore is normally expanded in large vertical chambers known as "expanders". At the bottom of each expander is a flame generating burner. The perlite ore to be expanded is dropped into the expander at a point above the flame and drops through the hot zone created by the flame. In this hot zone, the perlite particles expand and, because of their expanded volume, are then turned around and carried out of the top of the expansion chamber entrained in the exhaust gas stream. Operation of a typical perlite expander is shown in U.S. Patent No. 2,572,484 with another variation shown in U.S.
Patent No. ~,639,132.
It has been found over the years that the perlite ore, in order to be expanded satisfactorilyr must be in the form of particles or granules having a si~e of from about +2QO mesh (greater than 74 um) ~ ~ 6~S~3 up to approximately 3 to 4 mesh (approximately ~ inch or 6 mm). Larger partid es do not expand well because their weight pulls them through the flame zone too quickly for them to be heated to the expansion temperature and in addition their greater size and stronger structure prevents heat from penetrating to the center of the particle to convert the water to steam and also prevents the steam irom f~ly "popping" the large rigid particle. The presence of these larger particles in the perlite ore prior to e~panding causes no significant problems to the perlite ore processor, for such larger materials can be readily screened out of the raw material ore stream from the expanders and recycled to crushing or other size reduction equipment to reduce the large granules to the optimum size for expansion.
At the other end o the size scale, however, the material known as "ore fines" which have particle sizes not greater than 200 mesh (not greater than 74 um) do pose a significant problem for ~he ore processor. These materials do not expand well because their light weight and small size causes them to be entrained in the exiting air and gas stream in an expander before they have dropped far enough to encounter the appropriate temperature for expansion. In addition, such fine materials do not move well through the ore handling systems normally in use, which commonly rely in part on gravity feed.
Consequently, in the past, ore producers have considered the ore fines to be essentially waste material, although to some extent such unexpanded fine materials may find uses. Generally, however, since the largest market for perlite products is for expanded perlites, the ore processor is desirous of expanding as much of the ore raw material as possible~
It would be possible to handle such fine material if the individual fine particles were agglomerated into larger units which fall in the particle size range for conventional perlite eXpQnSiOn.
However, heretofore the known processes for agglomerating "perlite fines" have been processes intended to be used with previously expanded material. In the process of expansion, perlite (which is a somewhat brittle material) often shatters upon expansion leaving a substantial amount of fragments of expanded perlite. These fragments are themselves frequently referred to as "fines" but it must be ~mderstood that these are "expanded fines" as contrasted to the "ore fines" which :~3 5 ~ 3 are unexpanded and which are the subject of the present invention~
U~S. Patents Nos. 3~23S,635 and 4,175,158 both describe processes for agglomerating the expanded perlite fines by addition of water, a fluxing agent or, in the case of ~.S. Patent No. 4,175,158, boric acid. An integral part of both of these described processes, however, is heating and maintaining the expanded perlite fines at temperatures on the order of about 1200 to 1700F (650 to 925C). At these temperatures, the fluxing materials such as soda ash or B2O3 (from the boric oxide) act to fuse the expanded perlite fines into larger granules. Such processes are not applicable to ore fines of perlite, hcwever, because exposing the perlite ore to such temperatures will either cause the perlite to pop (if the exposure to the temperature is rapid) or will cause the water of hydration to slowly vaporize and be removed from the ore particle (if the perlite is slowly raised to that temperature) thus leaving no water of hydration to cause the perlite subsequently to pop.
It would therefore be highly desirable to have a process whereby the fine material in perlite ore raw materials can be agglomerated at relatively low temperatures to produce a particle of the appropriate size for conventional expansion.
Brief Summary of_the Invention The invention herein is a process for preparing perlite ore fines for expansion which comprises mixing the perlite ore fines with an agglomerating agent, the ~gglomerating agent having a viscous liquid phase at a temperature above room temperature but below the critical dehydration temperature of the perlite ore fines with the viscous liquid phase being capable of at least partially coating the perlite ore fines. m ereafter, the perlite ore fines are agglomerated by heating the mixture of the fines and the agglomerating agent to a temperature at which the agglomerating agent exists in the viscous liquid phase and maintaining the temperature for a period of time sufficient to obtain agglomeration of the fines by the agglomerating ayent.
In another aspect, the invention comprises preparing the perlite ore fines for expansion as described above followed by rapid heating of the prepared perlite ore fines to a temperature at which the perlite ore fines expand.
i J65513 ~ e pr~-fe~red ayglo~erating c~ents ~re n~aterials o the koron acid s~stem.
Detailed ~escrip-tion of ~h~ In-~entlon The pres~nt i~ven~ion involves ~he treating of perlite ore fines to r~3Xe th~ suitable for e~ ~nsion Ln a ~nvention~l perllte eYpander. The "ine" portion of -the Ferlite ore, as detel~Lned after the ore ras been oonventionally cleaned, crushed, screened and ~therwise made ready for expansion, is normLally defined as that portion of the ore which exists as particles having particle siæes of not greater -t~an 2C0 mesh (i.e., not greater than 7~ ~n). It will be understo~d, however, that there i5 no absolute and distinct dividlng line betwe,~n ~terials cons~dered "fines" and larger Ferlite particles considered to be conventional e.~,~indible p_rl~te. Thus, ~hile perlite havir,g particle sizes of not greater than 7~ um ( 200 mesh) is qenerally considered to constitute perlite ore fines, in some circumstances particles ~hi^h are larger than 74 um can also be considerea t~ be "fine". For instance, in mos~ conventional particle size sep2~a.or devices, there is not a sharp cut-off of particles at a s,pecifi0d si~e. ~ather -there is a distri~ution of particle sizes wit`n the princlpal seg~ent ~ing of t~e designated size but with ~e enti, e mass of s2plrat~d Ea~rticles ~lso containing scme material of larger and/or smaller size. Su~h i5 the case with ccmmercial perlite ore separation, ~here ~he "ore fines" fraction rlormally contains a portion havi~ E~u~ticle sizes above 74 um. m erefore, Sor the ~urposes of ~his invention, ~he "ore fines" wllich are beneficially agglc~nerated by the process o~ ~is invention will ~e definc~d as a nuLYture of perlite particles at least 50%, and preferably at least 70%, of whic~h have ExLrticle sizes of not greater than 74 um.
After ~he perlite ore fines (as defined a~ove) have been separated frGm the rem~inder of ~he perlite ore follcwm g conventional ~uning, drying, c~ shing, sizirlg and okher processes utili~ed in t~,e perlite ore produc-tion industry to prepare raw ma~erials for exFx~si~n, the fines are treatc~d in accordance with the present invention. They ar~ ~irst ~uLxed with a suitablr agglcmerating agent having t~e properties ~o be descri~ed ~elc~. Conveniently such agglcme..atillg agent is a colid material a~ amblent temperatures and mcst conveniently, the agglcme-rating agent has been ccmninuted into sQlid ~ ~65513 ~5--particles of approximately the sc~me particle size as the perlite ore fines. The perlite ore fines and agglomerating agent are blended and dry mixed by conventional mixing means such as rib~on blenders to form preferably a dry mixture of fines and agglomerating agent. Where the agglomerating asent is a liquid or has a liquid com~onent at ambient conditions, it is desirable to mix the fines and agglomerating agent and then dry the mixture to facilitate subsequent handling of the mixture.
The agglomerating agent will be a material which is compatible with perlite and which has a viscous liquid phase at ~
temperature above ambient temperature but below the dehydration temperature of the perlite. The viscous liquid phase must be one that will effect at least partial coating of the perlite ore fines with the liquid. Materials which have such liquid phases at the indicated temEeratures but which do not also effect such coating are not suitable for use in the present invention. Examples of such materials which have been tried but fo~nd not to work are hydrated sodi~n silicate and hydrated sodium carbonate ("soda ash"). The preferred materials which do mleet the required conditions are materials of the boron acid system, notably orthoboric acid (H3BQ3) and metaboric acid (HBO2).
Orthoboric acid is a colorless or white powder at ambient temperatures with a specific gravity of 1.43. At a temperature of approximately 340F (170C), orthoboric acid is transformed to metaboric acid.
Metaboric acid is a white crystalline solid at ambient temperatures 25 with a specific gravity of approximately 2.49. At approximately 460~F
(236C), the metaboric acid melts, forming a viscous liquid which may contain some crystals and which recrystallizes upon cooling. The phase change of metaboric acid from solid to liquicl at the melting point also results in approximately a 10-fold increase in the surface area. This liquid readily coats onto the perlite ore fine particles.
Descriptions of the boron acid system and the viscous metaboric acid liquid can be found in Kracek et al, "m e System, Water-Boron Oxide," er~ J~ Q~ Sci~, vol 35-A, pp. 143-171 (1938~; in De Bore (ed.), gs~s~,ie~ 5~ (1961) in the section by Dollimore et al, "m e Kinetics of the Thermal Decomposition of ~ome Substances Which Decompose to Oxides, and the Production of Active Solids by Such Processes" pp. 627-637; in Kemp, ~ t~ y~L~t~ B
~f' l 3 (1956), pp. 9-21; and in Kirk-Othmer (eds.), ~bçyclgeç~ f Cpemica Technology (3rd ednO, 1978), Vol. 4, pp~ 67-77.
rme agglomerating agent ~y be present in any amount from Q~1% to about 10% b~ weight based on the weight of the perlite ore fines, with the agent preferably being present as from 0.5 to 3 weight percent.
Following mixing of the perlite ore fines and the agglomerating agent, the blended materials are subjected to heating to a temperature at which the agglomerating agent is converted to the viscous liquid phase, but which temperature does not exceed the "critical dehydration temperature" of the perlite. For the purposes of this invention, the term "critical dehydration temperature" in fact represents time-temperature combinations. It is known that the ability of perlite to expand is based generally on essentially all of the bound water being simultaneously con~erted to steam, so that the expansion of the water on vaporization causes the perlite to expand as it seeks to escape from the particle. If, however, the bound water is vaporized slowly, each increment of vc~porized water will have time to diffuse or migrate slowly out of the unexpanded particle, ultimately leaving the perlite particle so depleted of water that rapid heating of the particle under normal expansion conditions will not result in expansion. m is slow "dehydration" of the particle ~which is "slaw" in comparison to the rate of the normal expansion-causing vaporiza'ion~
occurs at varying rates which are dependent on both the temperature to which the perlite is expo æd and also to the length of time of that exposure. As the temperature rises, the period of exposure time necessary to effect sufficient dehydration to prevent expansion is decreased. (At a sufficiently high temperaturer of course, vaporization occurs so rapidl~ and so uniformly across the particle that e~pansion is induced, since there is not sufficient time available to let the vaporized water escape from the particle by migration and/or diffusion~) In generalr at temperatures below about 1000F (540C), and especially below about 700F (370C), significant dehydration does not occur in the time periods required for the liquification and application of the agglom~rating agent. m erefore the effect of time can be simplified b~ merely requiring that the liquification and application of the agglomerating agent be conducted at a temFerature . 3 below the "critical deh~dration temperature," i.e., that temperature at which the time period of the liquification and application would be the minimum tLme in which significant dehydration could occur.
Normally the dry mixing and heating are done in separate but closely sequential steps. They could, however, be performed simultaneously by using a heated mixer. Alternatively, if the agglomerating agent is a stable material, mixing could take place long beEore heating with the mixed material simply being stored until time to be heated. m is would also permit the mixing and heating to be conducted at separate locations which are perhaps even quite remote from each other.
Tha time of maintenance at temperature is dependent upon the particular agglomerating agent being used. For the boron acids, it has been found that a time of 4 minutes at 600F (315C) provides quite satisfactory agglomeration of perlite fines. m e heating time should bé kept as short as possible commensurate with good agglomeration because of the tendency of the perlite to dehydrate over prolonged heating periods, even at relatively low temperatures. Heating times on the order of 1 to 20 minutes, preferably 3 to 10 minutes, are considered to be quite adequate.
In one aspect of the invention, the perlite ore fines ~hich have completed their heating with the agglomerating agent are passed directly to a perlite expander where they are expanded. This is quite feasible when the expander has associated therewith a pre-heat chamber into which the mixed perlite and agglomerating agent can be placed for heatin~. m e pre-heat chamber discharges into the expander feed system so that the agglomerated perlite ore fines can be fed directly to the expander for expansion. ~lternatively, however, the agglomerating agent will be one which can be cooled and then rapidly re-melted during expansion. mis would permit the perlite ore processor to agglomerate the ore fines with the agglomerating agent at the mine, mill or other ore producing or preparation site, then store or ship the agglomerated perlite ore fines to a remote location for exFansion with the agglomerated fines being put directly into the expander feed system without any further heating. This is the preferred manner of handling the heat treating and expansion. This is due to several factors: 1) Many perlite expanders are of rather small capacity and do not have .
S S ~ 3 heating equipment available in conjunction with the expander.
Consequently the processor wishing to use this proces~ in conjunction with perlite expansion would frequently be forced to add a heating unit at considerable cost to his perlite expansion equipment 2) Cnce the boric acid is coated on the perlike particles, the two components will not segregate as they would if they were merely blended into a simple dry mixtureO 3) A more uniform agglomerated fines product can be obtained, since the ore producer treats the perlite ore fines and thus can run a single consistent operation, rather than having a number of different end users treating perlite or fines in a variety of different types of mixers, heaters and under perhaps significantly different conditions. Such cooling, re-heating and remelting are quite feasible when orthoboric acid is used as the agg]omerating agent.
Once the perlite ore fines have been agglomerated with the agglomerating agent and heated for the appropriate time~ they are then ready to ~e expanded in a conventional perlite expander. As noted above, the expansion can come immediately after the heat treating or it can be delayed for any desired length of time. Expansion of the treated perlite ore fines is in the same manner as conventional perlite expansion of the larger normal perlite particles. me perlite ore fines can be expanded by themselves or can be mixed into a common feed with the original standard size perlite feed particles.
me examples below will illustrate the process of this invention. In these experiments, both the standard perlite ore materials and the perlite ore fines were from a commercial New Mexico perlite mining ~peration. Conventional mining, cleaning, crushing, sizing and other ore processing techniques were used. Agglomeration was with orthoboric acid in amounts of 1 or 2 percent by weight of the perlite ore fines, as noted. The fines portion of the ore was defined to be that portion in which 70~ of the particles were of 74 um particle size or smaller. ~eating of the ore fines/agglomerating agent mixture was for 4 minutes at 600F (315C). The 'ISeries A" runs illustrate the expansion of the perlite to the lowest achievable loose weight "Series B" are experiments in which the perlite was expanded to a loose weight in the range of 3 to 4 lb/ft3 (0.048 to 0.064 g/cm3), which is the conventional density for perlite use as an insulating filler~ The processing conditions were otherwise the same as in "Series A". "Loose 5 5 ~ 3 _g_ weight" is often referred to as l'bulk density" or "apparent densi~y"
and refers to the nominal density of a loosely packed powder.
T~ble 1 below shows the particle s,ize distributions o~ the pexlite ore fines and the standard ore as well as various expanded materials.
3 5 5 :1 3 o oO o ~ o~ ~ o ca C
a~ ~ 0~ o o o o~ ~ o w o ~ .~ o U C) ~ ~ r r ~ r ~ r~l r~
C
P~ Ed ~ ~Q
~ ~ ,~ r~ r~
~ 4 a) ~ a ~ ~ In O ~D O ~ -1 0 S_l r ~ ~ r_l r--l r~l ~ ~ r~ r~l dl ~, I¢ (~
V L l .r ~1 a~ O ~ ~ u~
S~.y O G~ a:~ ~ It'~ ~ ~ r-l i 1~
- . r ~ 3 - O
c 8 ~ ~ ~ o o o o u~
1~ L cn rl ~ D O
Ul~
~rC ' r q~ ~ ~5 ~ -1 0 CO u~ 1 h ~
O C ~
o o ~r o o o o o o o o ~ ~rl ~ ~ ~o o In æ ~ ~
~3 -10-.
~ ~S513 Table 2 below illustrates typical properties of the expanded materials. The "energy consumption" is the amount of energy required to expand the indicated material.
T~LE 2: _ S~RIE,S A
Loo~e_WQcLD~t Energy 3 3 ReCovery~ 5~i~ymE~iQ~aL
lb~f~ ~ç~_ ~ B~lb Non-agglomerated 2.1 0~034 83~3 23000 12800 Ore Fines Agglomerated 1O8 0.029 90.0 9940 5520 Fines (1%
boric acid) Agglomerated 1.67 0.027 94.5 13600 7560 Fines (2%
boric acid) Standard 1.62 0.026 92.9 18300 10200 Ore Note: (a) The data here are for a small (laboratory scale) expander.
The relative energy consumption per unit of perlite weight would be expected to be 8-10 times less for a commercial scale expander.
It will be evident from these experimental clata that the agglomerated perlite or fines expand to a size and loose weight essentially equivalent to that of standard perlite ore.
Similar data are presented in Tables 3 and 4 below for the "Series B" materials.
.
~ ~ O O C:~ ~ ~ ~ ~I ~ ~ ~ ~
c~ ~
r~
a ~ ~ a ~ o $a) u ~ tl) r~
l r ~ EL
rc ~3 r~
~ ~ ~ o OD ~r o r~ 1 o ~ C) r~
r ~ 3 ~:
CY L l ~r~
U~ (~ IL~ ~i ~_ a~ ~ o u~ 0 ~ ~ ~ ~1 1 0 4~
r ~ ~: r-l o a ~
~ aJ
c o a ~d . ~ ~ '` 0 o o ~
C40' I
,- rcl .
~ ~ a~ o co u~ I I r-l ~i rc~ -.a ~a ~ d ~ o o ~r o o o o o o o o ~ r~
~ a ~ u~ r~ o u~ o o o o ~ o . 1~ a~ ~
Ll l!~ r-l r-l ~ t~ ~ I N JJ
~u ~u~ æ
~3 -12-~yL~-9~ ERIEs B
__~Q~ Weight Energy 3 Recovery, Consume~ion~aL
~ t ~ _ % ~ Cal~
Non-agglomerated 3.5 U.056 89.1 15800 8740 Ore Fines Agglomerated 3.0 0.048 92.4 9080 5040 Fines (1%
boric acid) Agglomerated 3.5 0.056 94.4 7670 ~260 Fines (2%
boric acid) Standard 3~72 0.059 93.6 16200 9000 Ore Note: ~a) m e data here are for a small ~laboratory scalel expander.
The relative energy consumption per unit of perlite weight would be expected to be 8-10 times less for a commercial scale expander.
It will be evident Erom these data that the agglomerated fines of the process of this invention following expansion are equivalent to standard expanded perlite ore used for insulating fillers. In addition, the data from both Series A and Series B
indicate that the eneryy input required to expand the agglomerated fines is significantly less than that required to expand standard perlite ore. In addition, both the Series A and Series B experiments clearly indicate that the agglomerated perlite fines yield significantly greater recovery and significantly higher median particle si~es than the expanded perlite ore fines without any agglomeration.
The latter property is particularly significant since the value of an expanded perlite as an insulating or cement filler is directly proportional to the particle size of the perlite.
~:16~3 1~--e~
m e invention herein relates to ~he perlite expansion industry. It is particularly useful in the expansion of the fine portion of perlite ore~ Expanded perlite ores find utility as thermal insulations in such materials as structural roofing boards and insulating wall boards for residential, commercial and industrial buildings. Expanded perlite also finds considerable use as a light weight aggregate for construction materials such as plaster, gypsum and concrete. Construction panels made of the materials containing light weight aggregates are used where strength is not a prime requirement but where fire resi~tance, insulation and light weiyht are major considerations. Typical applications include instalJation in tall buildings and long span bridges.
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for preparing perlite ore fines for expansion which comprises mixing said perlite ore fines with an agglomerating agent which has a viscous liquid phase at a temperature above ambient temperature but below the critical dehydration temperature of said perlite ore fines, heating the mixture of said ore fines and agglomerating agent to a temperature at which said agglomerating agent exists as said viscous liquid phase and below the critical dehydration temperature of the perlite ore fines, maintaining said temperature for a period of time sufficient to obtain a viscous agglomeration of said perlite ore fines and said agglomerating agent, cooling said viscous agglomeration so that said perlite ore fines have at least a partial coating of said agglomerating agent thereon; heating said coated perlite ore fines to a temperature at which said agglomerating agent exists as said viscous liquid phase and then applying more heat to expand said perlite ore fines into expanded perlite of conventional size and density.
2. A process as in Claim 1 wherein said agglomerating agent is a member of the boron acid system.
3. A process as in Claim 2 wherein the member of the boron acid system is a boric acid selected from the group consisting of orthoboric acid and metaboric acid.
4. A process as in Claim 3 wherein the mixture of the agglomerating agent and the perlite ore fines is heated to a temperature which is above the melting point of the agglomerating agent and is less than about 1000°F for a period of time from about 1 to about 20 minutes.
5. A process as in Claim 3 wherein the boric acid is utilized in an amount of from about 0.1 to about 10 percent by weight based on the weight of the perlite ore fines.
6. A process as in Claim 5 wherein the mixture of the boric acid and perlite ore fines is heated to a temperature above the melting point of the boric acid and less than about 700°F for a time period of from about 3 to 10 minutes.
7. A process as in Claim 6 wherein the boric acid is orthoboric acid.
8. A process as in Claim 7 wherein the boric avid is transformed to metaboric acid during the process.
9. A process as in Claim 6 wherein the boric acid is metaboric acid.
10. A process as in Claim 6 wherein said perlite ore fines comprise a mixture of perlite ore particles at least 50% of which have particle sizes of not greater than 74 um.
11. A process as in Claim 6 wherein said perlite ore fines comprise a mixture of perlite ore particles at leat 70% of which have particle sizes of not greater than 74 um.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US17042480A | 1980-07-21 | 1980-07-21 | |
| US06/170,424 | 1980-07-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1165513A true CA1165513A (en) | 1984-04-17 |
Family
ID=22619796
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000382050A Expired CA1165513A (en) | 1980-07-21 | 1981-07-20 | Preparation and expansion of perlite ore fines |
Country Status (4)
| Country | Link |
|---|---|
| BE (1) | BE889679A (en) |
| CA (1) | CA1165513A (en) |
| FR (1) | FR2486929B1 (en) |
| GB (1) | GB2080282B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2016178906A1 (en) * | 2015-05-01 | 2016-11-10 | Imerys Filtration Minerals, Inc. | Methods for strengthening perlite microspheres, and fluids and cements including strengthened perlite microspheres |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0086248A1 (en) * | 1982-02-17 | 1983-08-24 | Bernd Dr. Wüstefeld | Fine-grained expanded granule and method for producing it |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE387747C (en) * | 1920-10-07 | 1924-01-04 | Alexandre Bigot | Process for the production of porous artificial stones |
| US1842875A (en) * | 1927-12-14 | 1932-01-26 | Harvey B Lindsay | Thermal insulating structure and method of manufacturing same |
| US3271323A (en) * | 1961-04-03 | 1966-09-06 | Norton Co | Silicate minerals having increased surface area and absorption properties and methodof preparation thereof |
| US3961978A (en) * | 1974-09-20 | 1976-06-08 | General Refractories Company | Process for producing perlite microspheres |
-
1981
- 1981-07-16 GB GB8122019A patent/GB2080282B/en not_active Expired
- 1981-07-20 FR FR8114078A patent/FR2486929B1/en not_active Expired
- 1981-07-20 CA CA000382050A patent/CA1165513A/en not_active Expired
- 1981-07-20 BE BE0/205445A patent/BE889679A/en not_active IP Right Cessation
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2016178906A1 (en) * | 2015-05-01 | 2016-11-10 | Imerys Filtration Minerals, Inc. | Methods for strengthening perlite microspheres, and fluids and cements including strengthened perlite microspheres |
Also Published As
| Publication number | Publication date |
|---|---|
| BE889679A (en) | 1982-01-20 |
| GB2080282B (en) | 1983-11-23 |
| FR2486929B1 (en) | 1986-02-21 |
| FR2486929A1 (en) | 1982-01-22 |
| GB2080282A (en) | 1982-02-03 |
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