Method of recovering minerals from papermaking sludge and sludge-derived ash

Extraction of minerals from papermaking sludge or sludge-derived ash is accomplished by mixing with a solution of an inorganic or organic acid--generally 0.1% to 35% by weight, preferably 2% to 20%, and most preferably 3% to 8% by weight. In preferred embodiments, the material is carried as an aqueous solution and combined with 2% to 20%, and most preferably 3% to 6%, HCl; 2% to 25%, and most preferably 8%, HNO.sub.3 ; 2% to 30%, and most preferably 8%, acetic acid. Generally, the amount of acid added into the reaction mixture preferably is 0.8 to 2.0 times the stoichiometric calcium carbonate content in the mixture, more preferably 0.8 to 1.2 times the stoichiometric content, and most preferably matched to the stoichiometric content of calcium carbonate in the mixture. The acid-containing mixture is incubated (with agitation, if desired, to shorten the reaction time) to solubilize the desired minerals, following which the liquid phase is isolated, and mineral salts recovered therefrom.

FIELD OF THE INVENTION 
The present invention relates to utilization of renewable resources and 
industrial wastes, such as pulp and paper sludge and products of their 
incineration, and in particular to recovery of minerals from these 
materials. 
BACKGROUND OF THE INVENTION 
Pulp and paper sludge (a byproduct of primary pulping operations, recycle 
streams or waste paper pulping and the like), as well as the products of 
its incineration, represent an environmental and disposal problem for 
manufacturers of pulp and paper. Generally, pulp and paper sludge is 
unsuitable for paper making, although it generally includes the same 
components--lignin, cellulose, hemicellulose, calcium carbonate, clay, and 
other inorganic components--as those present in the paper pulp itself. 
Paper sludge has traditionally been disposed of by landfilling, composting, 
utilization by the cement industry, and by incineration. The latter 
option, in turn, creates another problem, namely, disposal of the 
resulting ash, which often constitutes up to 50% (and sometimes as much as 
80% or higher) of the volume of the sludge itself. Calcium carbonate, in 
the form of precipitated calcium carbonate (PCC) or ground calcium 
carbonate (GCC), typically constitutes 20% and up to 75% of dry sludge 
content. Calcium carbonate is a natural carbonate which is loaded, 
typically together with clay, into paper as a coating and filler to 
improve the mechanical characteristics as well as the appearance of paper. 
Despite their natural abundance, calcium salts are generally expensive 
products because of the difficulties and expenses of their purification 
from natural mineral deposits. For instance, paper-quality PCC is 
typically produced from natural limestone via many stages including the 
calcination of limestone in an industrial kiln (into either a calcitic or 
a dolomitic lime), slaking, slurrying, carbonating, and a number of 
refining steps. 
Calcium-derived compounds undergo chemical changes when paper sludge is 
incinerated. These changes were outlined in recent articles (see Sohara, 
"Recycling Mineral Fillers from Deinking Sludges," Paper Recycling '96 
Conf. 1996) (hereafter "Sohara"); Pera et al., "Paper Mill Sludge: A 
Source of Valuable Cement Additives," Paper Recycling '96 Conf. (1996). 
The organic components of sludge are completely destroyed during 
incineration. Thermal dehydration of clay results in calcined 
aluminosilicates, which form complex chemical compounds with 
decarboxylated calcium carbonate of general formula Ca.sub.n Al.sub.a 
Si.sub.b O.sub.c, that is, calcium aluminosilicates. Silica, which enters 
the thermally treated sludge from the fluidizing medium (sand) during the 
incineration process and also as a product of kaolin thermal breakdown, 
reacts with calcium oxide (derived from thermal decarboxylation of calcium 
carbonate) forming calcium silicate CaSiO.sub.3. Other minerals present in 
sludges (as pigments, fillers, traces of flocculants, etc.), such as those 
based on magnesium, potassium, titanium and others, make the composition 
of the mineral content even more complex. The particular species formed 
depends mainly upon the relative amount (and nature) of clay in the 
mineral fraction of the sludge, the amount of calcium carbonate, and the 
conditions of the thermal treatment. 
Formation of calcium silicates in the course of incineration of 
lime-treated "green liquor" residues, containing calcium carbonate and 
silica, was described in Chattaraj et al., Indian Pulp & Paper, June-July 
1981, at 21-28. Such an incineration leads to the formation of di- and 
tri-calcium silicates (presumably, larnite Ca.sub.2 SiO.sub.4 and 
gehlenite Ca.sub.2 Al.sub.2 SiO.sub.7 among them), which in turn form a 
fine gelatinous precipitate of calcium silicate dihydrate in the caustic 
liquor ("white liquor"). The authors reported that calcium silicates make 
calcination of calcium carbonate more difficult. Moreover, calcium 
silicate particles that are formed as a result of the calcination process 
are fused into irregularly shaped abrasive agglomerates unsuitable for 
paper filling and coating; see Johnston et al., Appita Journal, 
49(6):397-402 (1996). 
Unfortunately, the inorganic content of sludge and sludge-derived ash is 
generally largely or totally wasted. At best, the prior art describes 
utilization of incineration ash for production of low-end, impure products 
of limited market value. For example, Sohara details processing of such 
ash to precipitate calcium carbonate on the surface of the ash itself 
(without separation from the ash). In particular, an aqueous slurry of 
incineration ash is carbonated with carbon dioxide gas; calcium carbonate 
nucleates and grows during the precipitation reaction. The resulting 
mixture of precipitated calcium carbonate and ash still contains from 10% 
to 30% incineration ash, and represents an undifferentiated agglomeration 
of minerals and clay. 
Lacking in the prior art is a cost-effective method of producing pure, 
high-grade calcium and other mineral salts from papermaking sludge or ash 
derived therefrom. 
DESCRIPTION OF THE INVENTION 
BRIEF SUMMARY OF THE INVENTION 
The invention provides a method of obtaining minerals from papermaking 
sludge (pressed or dried) or incinerated sludge (ash) notwithstanding the 
various chemical changes that occur during incineration. The invention 
involves combination of the pressed or dried sludge or sludge-derived ash 
with a diluted acid, following which the solid content is separated from 
the liquid content to obtain a solids-free solution of the calcium salt. 
The separation of the liquid from the solid residue is preferably carried 
out using belt presses, screw presses, centrifuges, filters, or a 
combination. The solids obtained can be further washed with water in order 
to increase the yield of the calcium salt. 
The invention can be practiced using virtually any acid that reacts with 
solid CaCO.sub.3 to produce an aqueous calcium salt. Suitable examples 
include hydrochloric acid, nitric acid, and acetic acid. In one embodiment 
of the invention, precipitated CaCO.sub.3 is obtained from the solids-free 
liquid fraction using carbon dioxide gas, as described in U.S. Pat. Nos. 
5,007,964 and 5,376,343; or by other means, as described in U.S. Pat. No. 
4,100,264. The '964, '343 and '264 patents are hereby incorporated by 
reference in their entireties. 
Papermaking sludge typically contains a rather high amount of CaCO.sub.3 
(up to 20%-50% of solids or more). In the presence of many acids, 
CaCO.sub.3 is solubilized as a result of conversion into the acid-anion 
salt in the reaction mixture. Since papermaking sludge often contains an 
organic fraction (cellulose, lignin, hemicellulose), some organic 
materials, pentose sugars in particular, can be extracted by acids as 
well, thereby decreasing the purity of the target calcium salt. Also, 
CaCO.sub.3 in the sludge is typically accompanied by aluminosilicates 
(clay) and other minerals (as pigments, fillers, etc.), such as those 
based on magnesium, potassium and others. These can be partially extracted 
with acids as well. Obviously, the extent of acid 
extraction/solubilization of the inorganic and organic components, making 
the target calcium salt less pure, greatly depends on conditions of the 
sludge treatment with acids, nature of the acid, the acid concentration, 
and contact time with the acid in particular. 
Combustion (calcination, or incineration) of sludge eliminates the organic 
components of the material and makes the material more compact. However, 
this process may also change the chemistry of the inorganic constituents. 
Calcination of CaCO.sub.3 in the presence of aluminosilicates, for 
example, leads to formation of calcium aluminosilicates and other complex 
minerals (see above). Their chemical properties differ significantly from 
those of calcium carbonate, as illustrated by the following comparative 
examples. 
Comparative Example 1. Five types of materials were tested for their 
alkalinity, that is their ability to increase pH of water in standard 
conditions (10 mg/10 mL at room temperature): 
(1) CaO (commercial preparation), 
(2) CaCO.sub.3 (commercial preparation), 
(3) CaCO.sub.3, calcined at 825.degree. C., 900.degree. C., and 
1000.degree. C. (weight loss 44.0.+-.0.4% compare with the initial 
CaCO.sub.3), 
(4) Dry paper sludge (CaCO.sub.3 content 23%, total ash content 32.7%), and 
(5) Paper sludge as in (4), but calcined at 825.degree. C., 900.degree. C., 
and 1000.degree. C. (weight loss 24.0.+-.0.4%); calcium content 
30.0.+-.0.4%, which translates into 42.0.+-.0.6% CaO equivalent. 
Dry paper sludge (4) and pure CaCO.sub.3 (2) showed similar alkalinity: the 
pH increased to 9.2-9.6, though it took more time and/or a higher amount 
for the sludge to reach the same pH value as CaCO.sub.3. 
Calcined CaCO.sub.3 (all three samples, calcined at the temperatures 
indicated above) showed the same alkalinity as pure CaO: all produced a 
rapid "pH-jump" to 12.6-12.7. Even 20% of the amount taken, i.e., 2 mg of 
CaO, produced a rapid pH increase to 12.0. 
Calcined sludge (all three samples, calcined at the temperatures indicated 
above) produced rather slow increase in pH, and only to 10.9-11.2. 
This Example shows that the calcined paper sludge does not contain CaO. 
Besides, calcium compound(s), formed as a result of calcination of the 
sludge, are obviously less reactive than calcium oxide. 
Comparative Example 2. Three types of materials were tested for their 
exothermic reactivity upon contact with water, i.e., their ability to 
increase temperature of water in standard conditions (0.5 g/0.5 mL, 
starting at room temperature): 
(1) CaO (commercial preparation), 
(2) CaCO.sub.3, calcined at 1000.degree. C., 
(3) Calcined paper sludge as in Comparative Example 1 (calcined at 
825.degree. C. and 1000.degree. C., calcium content 30.0.+-.0.4%, 
translating into 42.0.+-.0.6% of CaO equivalent). 
Freshly calcined CaCO.sub.3 showed the highest exothermic effect, 
temperature 86.5.degree. C. was reached in 40 seconds. 
Commercial CaO showed increase in temperature up to a maximum at 59.degree. 
C. reached in 10.5 min. 
Calcined sludge did not show any noticeable increase in temperature (i.e., 
less than 0.5. 
This Example shows again that the calcined paper sludge does not contain 
CaO. Besides, calcium compound(s), formed as a result of calcination of 
the sludge, obviously are quite different chemical(s) from calcium oxide. 
In a first aspect, the invention comprises extraction of minerals from a 
papermaking sludge. The sludge generally contains a mix of common 
components of plant materials with minerals (CaCO.sub.3 and clay, in 
particular, that typically can account for a significant fraction of the 
composition of paper sludge), and is mixed with a solution of an inorganic 
or organic acid--generally 0.1% to 35% by weight, preferably 2% to 20%, 
and most preferably 3% to 8% by weight; the optimal concentration depends 
on process conditions (in particular, calcium carbonate content in the 
processed papermaking sludge) and the desirable concentration of the 
target salt in the solution produced. In preferred embodiments, the 
mixture is combined with 3% to 6% HCl; 2% to 25%, and most preferably 8%, 
HNO.sub.3 ; 2% to 30%, and most preferably 8%, acetic acid. Generally, the 
amount of acid added into the reaction mixture preferably is 0.8 to 2.0 
times the stoichiometric calcium carbonate content in the mixture, more 
preferably 0.8 to 1.2 times the stoichiometric content, and most 
preferably matched to the stoichiometric content of calcium carbonate in 
the mixture. The acid-containing mixture is incubated (with agitation, if 
desired, to shorten the reaction time) to solubilize the desired minerals, 
following which the liquid phase is isolated, and mineral salts recovered 
therefrom. 
In a second aspect, the invention comprises extraction of minerals from ash 
produced by incineration of a papermaking sludge. The ash is combined with 
water and mixed with a solution of an inorganic or organic acid--generally 
2% to 35% by weight, preferably 5% to 25%, and most preferably 8% to 14% 
by weight; the optimal concentration depends on process conditions (in 
particular, calcium carbonate content in the ash) and the desirable 
concentration of the target salt in the solution produced. In preferred 
embodiments, the mixture is combined with 8% to 14% HCl; 5% to 20%, and 
most preferably 8% to 10%, HNO.sub.3 ; 5% to 20%, and most preferably 10% 
to 13%, acetic acid. Generally, the amount of acid added into the reaction 
mixture preferably is 0.8 to 2.0 times the stoichiometric calcium 
carbonate content in the mixture, more preferably 0.8 to 1.2 times the 
stoichiometric content, and most preferably matched to the stoichiometric 
content of calcium carbonate in the mixture. Once again, the 
acid-containing mixture is incubated (with agitation, if desired, to 
shorten the reaction time) to solubilize the desired minerals, following 
which the liquid phase is isolated, and mineral salts recovered therefrom. 
After completion of calcium solubilization, which can be verified by 
determination of the calcium concentration or content in the bulk 
solution, the liquid is separated from the solids by conventional means, 
such as filtration, centrifugation, or dewatering using belt presses, 
screw presses, filters and the like, or other suitable separation method. 
The solid residue comprising cellulose fiber, lignin, and minerals, such 
as clay, kaolin, other aluminosilicates, etc., can be utilized in other 
applications, serving as cat litter or an oil absorbant. 
The calcium salt obtained in the liquid is used in the form of that liquid 
or in a concentrated form (e.g., by evaporation of the water phase), or 
recovered by precipitation as a water-insoluble calcium compound, e.g., 
calcium carbonate. The precipitation is performed using water-soluble 
carbonates or bicarbonates, or by carbonation of the water solution with 
carbon dioxide, or by any other suitable carbonation method. Using 
different carbonation methods (e.g., at different temperatures), different 
concentrations of water-soluble calcium salts, different flow rate of 
carbon dioxide, etc., different morphological forms of calcium carbonate 
are produced as precipitates for use in the many known applications of 
calcium carbonate. 
Using the approach of the present invention, it is possible to obtain 
solutions of calcium chloride, calcium nitrate, and calcium acetate from a 
number of papermaking sludge materials, and a number of their incineration 
ash preparations obtained at various thermal conditions. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
EXPERIMENTAL PROCEDURES 
1. Determination of calcium: the procedure based on titration with EDTA 
TAPPI procedure T 247 cm-83 (Classical Method-1983) was used for calcium 
determination in sludge and pulp. The procedure is based on EDTA titration 
of HNO.sub.3 - soluble calcium in ashed sludge and pulp. EDTA forms a 
highly-colored water-soluble complex with calcium, while other metal ions 
present are masked with triethanolamine. The ash was placed in 10 mL of 
Milli-Q and 3 mL of 5 M nitric acid (325 mL of concentrated nitric acid 
diluted to 1 L with water) was added. The mixture was heated for 5-10 min 
on a steam bath, transferred into a 300-mL flask, the volume was adjusted 
to 100 mL, 5 mL of 8 M KOH solution was added, the flask was shaken 
occasionally for 5 min, and 5 mL of triethanolamine (diluted 10 times), 
and then 2 mL of hydroxylamine hydrochloride solution (2 g/100 mL) were 
added, along with 100 mg of cal-red indicator. The mixture was titrated 
with 0.02 M EDTA solution to a color change from red-wine to blue. Calcium 
content (in %) was calculated as EDTA(mL).times.0.08016/g of dry weight 
ash. 
2. Determination of solids and calcium content in acid calcium extracts, 
dried at 105.degree. C. and combusted at 525.degree. C. 
Weight determination of compounds dissolved in acid water extracts, 
described below as "solids," was performed by evaporation of a 10-mL 
sample at 105.degree. C.--until a constant weight was attained--using the 
Mettler Infrared Moisture Analyzer, or a programmable oven. 
Salts of calcium and other metals, typically present in acid extracts of 
papermaking sludge, often contain bound water. Since this water often 
remains with salts dried at 105.degree. C., calcium (as well as other 
metals) are typically "diluted" when determined in the dried extracts. 
Examples of such calcium salts include: CaCl.sub.2.H.sub.2 O, 
CaCl.sub.2.2H.sub.2 O (loses both water molecules at 200.degree. C.), 
calcium chloride aluminate 3CaO.Al.sub.2 O.sub.3.CaCl.sub.2.10H.sub.2 O 
(loses 1 water molecule at 105.degree. C. and 8 water molecules at 
350.degree. C.), Ca(NO.sub.3).sub.2.3H.sub.2 O, 
Ca(NO.sub.3).sub.2.4H.sub.2 O water at 132.degree. C.), Ca(CH.sub.3 
COO).sub.2.2H.sub.2 O (loses 1 water molecule at 84.degree. C.), 
Ca(CH.sub.3 COO) .sub.2.H.sub.2 O (loses the water molecule at about 
150.degree. C., converts into CaCO.sub.3 at 160.degree. C.), 
CaCO.sub.3.6H.sub.2 O. If not taken into consideration, these bound water 
molecules affect analytical results. Some other bound water-containing 
compounds that might easily get into the sludge acid-extracted solids and 
their carbonated precipitates, and therefore affect analytical data, are 
Mg(CH.sub.3 COO).sub.2.4H.sub.2 O, Mg(CO.sub.3).3H.sub.2 O, 
Mg(CO.sub.3).5H.sub.2 O, and others. 
To eliminate the bound water as much as possible without substantially 
altering the principal chemical composition of the solids, the solids were 
dried at 105.degree. C., analyzed, and then combusted at 525.degree. C. 
Reduction in weight as a result of the combustion was typically ascribed 
either to a combination of organic materials and bound water (when a whole 
sludge extracts were analyzed), or to bound water alone (when extracts of 
the ashed sludge were analyzed). Calcium acetate on heating above 
160.degree. C. decomposes to CaCO.sub.3 and acetone. Therefore, calcium 
content in the combusted solids, extracted with acetic acid, can be 
indicative of the purity of the originally solubilized calcium acetate. 
For example, if elemental calcium content in the combusted solids is 40% 
by weight (corresponding to pure CaCO.sub.3), the acetic acid calcium 
extract contains practically pure calcium acetate. 
Calcium in the acid extracts dried at 105.degree. C. and 525.degree. C. was 
determined using TAPPI procedure T 247 cm-83, as described above. Calcium 
in liquid acid extracts was determined in 1-mL or 3-mL aliquots also 
processed according to said TAPPI procedure.

EXAMPLE 1 
This example describes solubilization of calcium (in the form of calcium 
chloride) from mixed office sludge by diluted hydrochloric acid, in a 
proportion of 1.56 times the stoichiometric amount of calcium carbonate 
content in the sludge. The initial sludge material had a moisture content 
of 43.4%, an ash content of 32.7% (dry matter), and an elemental calcium 
content of 9.2%, representing a calcium carbonate content of 23% in the 
whole dried sludge. Moisture content was determined either by heating the 
material in a temperature-programmed furnace at 105.degree. C. to constant 
weight, typically overnight, or using a Mettler Moisture Analyzer. Ash 
content was determined by combustion of the material overnight in a 
furnace at 525.degree. C. 
The solubilization was performed as follows. 33.4 mL (39.75 g) of 37.4% 
hydrochloric acid was added to 116.6 mL of water, and the resulting 150 mL 
of 8.3% (v/v) or 9.9% (w/w) HCl was added to 100 g of the wet sludge 
(taking into account water content in the sludge, the final concentration 
of HCl in the liquid was 6.5% v/v, or 7.7% w/w). That amount of 
hydrochloric acid was 56% higher compared with the stoichiometric amount 
needed for complete solubilization of the calcium carbonate present in the 
sludge. The mixture was placed in an incubator-shaker, and incubated for 4 
hrs at 500 rpm, room temperature. Supernatant was then decanted, the solid 
residue pressed, and 118 mL of liquid was collected. The liquid contained 
10.6% of solids, as was shown by evaporation of a 5-mL sample at 
105.degree. C. 
Elemental calcium content in the dried solids was 25.7%, translating into 
71.3% of CaCl.sub.2, or 94.4% of CaCl.sub.2.2H.sub.2 O of the total 
solids. 
Elemental calcium content in the liquid extract was 27,570 ppm, or 2.76%. 
This translates into 7.65% of CaCl.sub.2 or 10.13% of CaCl.sub.2.2H.sub.2 
O in the extract, that is, 72.2% and 95.6% of total solids, respectively. 
Combustion of the dried solids at 525.degree. C. reduced their weight by 
19.2% (the theoretical value for transition of CaCl.sub.2.2H.sub.2 O into 
CaCl.sub.2 is 24.5%), and the calcium content in the combusted solids was 
determined to be 28.7%, translating into 80% of CaCl.sub.2 in the total 
solids. 
41.3 g of the washed and dried sludge residue was collected. The calcium 
content in the solid residue was 0.8%. The material contained primarily 
cellulose, lignin, and clay. 
The following Table 1 shows analysis of the liquid obtained as in Example 
1. 
TABLE 1 
______________________________________ 
Analysis of calcium chloride solution, obtained by solubilization of 
calcium from mixed office paper sludge with hydrochloric acid (1.56 
times the stoichiometric calcium carbonate content in the sludge) 
Analysis ppm (mg/L) 
% of Ca content 
______________________________________ 
Calcium 25,300 100.00 
Aluminum 514 2.03 
Magnesium 430 1.70 
Silicon 130 0.51 
Iron 68 0.27 
Potassium 17 0.07 
Heavy Metals as Lead 
&lt;30 &lt;0.12 
Titanium 0.88 0.003 
Organic Carbon 1,032 4.08 
Chloride 68,000 
Calcium Chloride 
106,000 
______________________________________ 
EXAMPLES 2 AND 3 
The procedure of Example 1 was repeated, but with the difference that the 
amount of hydrochloric acid added to the sludge was the 1.2 times the 
stoichiometric calcium carbonate content in the sludge. Two separate 
experiments were performed, one with 100 g of the wet sludge, another with 
250 g of the wet sludge. 
(EXAMPLE 2) 24.9 mL (29.63 g) of 37.4% HCl was added to 125.1 mL of water, 
and the resulting 150 mL of 6.2% (v/v) or 7.2% (w/w) HCl was added to 100 
g of the wet sludge (taking into account water content in the sludge, the 
final concentration of HCl in the liquid was 4.8% v/v, or 5.6% w/w). 
Incubation of the reaction mixture in the incubator-shaker took place for 
30 min at 500 rpm. 121 mL of liquid was collected. The liquid contained 
7.7% of solids (dried at 105.degree. C.). Elemental calcium content in the 
dried solids was 30.0%, translating into 83% CaCl, or 110% 
CaCl.sub.2.2H.sub.2 O relative to the total solids. 
Combustion of the dried solids at 525.degree. C. reduced their weight by 
13.9% (the theoretical value for transition of CaCl.sub.2.2H.sub.2 O into 
CaCl.sub.2 is 24.5%), and the calcium content in the combusted solids was 
determined to be 33.6%, translating into 93% of CaCl.sub.2 in the total 
solids. 
(EXAMPLE 3) 63.0 mL (75.0 g) of 37.4% HCl was added to 437 mL of water, and 
the resulting 500 mL of 4.7% (v/v) or 5.5% (w/w) HCl was added to 250 g of 
the wet sludge (taking into account water content in the sludge, the final 
concentration of HCl in the liquid was 3.9% v/v, or 4.5% w/w). The mixture 
was agitated with a propeller mixer for 30 min. 440 mL of liquid was 
collected. The liquid contained 8.2% solids (dried at 105.degree. C.). 
Elemental calcium content in the dried solids was 26.2%, translating into 
73% CaCl, or 96% CaCl.sub.2.2H.sub.2 O relative to the total solids. 
Combustion of the dried solids at 525.degree. C. reduced their weight by 
17.5% (the theoretical value for transition of CaCl.sub.2.2H.sub.2 O into 
CaCl.sub.2 is 24.5%), and the calcium content in the combusted solids was 
determined to be 33.6%, translating into 93% CaCl.sub.2 in the total 
solids. 
102.7 g of the unwashed and dried sludge residue was collected, with an 
average calcium content 4.9%. Washing of the residue with 5-fold excess of 
water resulted in 98%-recovery of the solid residue and 99%-recovery of 
wash waters, with solids content 0.58%. Drying at 105.degree. C. 
(wash-water temperature) resulted in solids having a calcium content 
30.3%, translating into 84% CaCl.sub.2, or 111% CaCl.sub.2.2H.sub.2 O. 
EXAMPLES 4 AND 5 
The procedure of Example 1 was repeated, but with the difference that the 
amount of hydrochloric acid added to the sludge was stoichiometric with 
respect to the calcium carbonate content in the sludge. 
(EXAMPLE 4) 21.4 mL (25.45 g) of 37.4% HCl was added to 128.6 mL of water, 
and the resulting 150 mL of 5.3% (v/v) or 6.3% (w/w) HCl was added to 100 
g of the wet sludge (taking into account water content in the sludge, the 
final concentration of HCl in the liquid was 4.1% v/v, or 4.9% w/w). The 
reaction mixture was placed into an incubator-shaker for 30 min at 300 
rpm. 115 mL of liquid was collected. The liquid contained 6.9.+-.0.2% of 
solids (representing the average of two separate drying procedures at 
105.degree. C.). Elemental calcium content in the dried solids was 
determined to be 29.8%, translating into 83% CaCl.sub.2, or 110% 
CaCl.sub.2.2H.sub.2 O. 
Combustion of the dried solids at 525.degree. C. reduced their weight by 
18.6% (the theoretical value for transition of CaCl.sub.2.2H.sub.2 O into 
CaCl.sub.2 is 24.5%), and the calcium content in the combusted solids was 
determined to be 31.8%, translating into 88% of CaCl.sub.2 in the total 
solids. 43.2 g of the washed and dried sludge residue was collected. The 
calcium content in the solid residue was determined to be 2.6%. 
(EXAMPLE 5) 51.9 mL (61.8 g) of 37.4% HCl was added to 448.1 mL, of water, 
and the resulting 500 mL of 3.9% (v/v) or 4.5% (w/w) HCl was added to 250 
g of the wet sludge (taking into account water content in the sludge, the 
final concentration of HCl in the liquid was 3.2% v/v, or 3.7% w/w). The 
mixture was agitated with a propeller mixer for 30 min. 400 mL of liquid 
was collected. The liquid contained 5.9% solids (dried at 105.degree. C.). 
Elemental calcium content in the dried solids was determined to be 28.7%, 
translating into 80% CaCl, or 105% CaCl.sub.2.2H.sub.2 O relative to the 
total solids. 
Combustion of the dried solids at 525.degree. C. reduced their weight by 
14.4% (the theoretical value for transition of CaCl.sub.2.2H.sub.2 O into 
CaCl.sub.2 is 24.5%), and the calcium content of the combusted solids was 
determined to be 32.9%, translating into 91% of CaCl.sub.2 in the total 
solids. 
97.3 g of the unwashed and dried sludge residue was collected, with an 
average calcium content of 6.6%. Washing of the residue with a 5-fold 
excess of water resulted in 98% recovery of both the solid residue and the 
wash waters. Elemental calcium content of the solid residue, dried at 
105.degree. C., was determined to be 4.7%. Drying of the wash waters at 
105.degree. C. resulted in solids (0.53% by weight) with calcium content 
of 30.1%, translating into 84% CaCl.sub.2, or 111% CaCl.sub.2.2H.sub.2 O. 
The following Table 2 shows analysis of the liquid obtained as in Example 
4. 
TABLE 2 
______________________________________ 
Analysis of calcium chloride solution, obtained by solubilization of 
calcium from mixed office paper sludge with HCl (the stoichiometric 
amount of the acid relative to calcium carbonate content 
in the sludge was used) 
Analysis ppm (mg/L) 
% of Ca content 
______________________________________ 
Calcium 32,820 100.00 
Aluminum 276 0.84 
Magnesium 338 1.03 
Silicon 99 0.30 
Iron 34 0.10 
Potassium 21 0.06 
Heavy Metals as Lead 
&lt;30 &lt;0.09 
Titanium 0.17 0.0005 
Organic Carbon 765 2.33 
Chloride 44,200 
Calcium Chloride 
69,200 
______________________________________ 
EXAMPLES 6 AND 7 
The procedure of Example 1 was repeated, but with the difference that the 
amount of HCl added to the sludge was the 0.8 times the stoichiometric 
calcium carbonate content in the sludge. 
(EXAMPLE 6) 16.6 mL (19.75 g) of 37.4% HCl was added to 133.4 mL of water, 
and the resulting 150 mL of 4.1% (v/v) or 4.9% (w/w) HCl was added to 100 
g of the wet sludge (taking into account the water content of the sludge, 
the final concentration of HCl in the liquid was 3.2% v/v, or 3.8% w/w). 
The reaction mixture was placed into an incubator-shaker for 30 min at 500 
rpm. 125 mL of liquid was collected. The liquid contained 5.9% solids 
(dried at 105.degree. C.). Elemental calcium content in the dried solids 
was 31.6%, translating into 88% CaCl, or 116% CaCl.sub.2.2H.sub.2 O 
relative to the total solids. 
Combustion of the dried solids at 525.degree. C. reduced their weight by 
18.6% (the theoretical value for transition of CaCl.sub.2.2H.sub.2 O into 
CaCl.sub.2 is 24.5%), and calcium content in the combusted solids was 
determined to be 32.8%, translating into 91% of CaCl.sub.2 in the total 
solids. 
48.53 g of the unwashed and dried sludge residue was collected, with an 
average calcium content 5.7%; washing with 250 mL of water resulted in 
48.03 g of washed dry material with a calcium content of 3.0%. 245 mL of 
wash waters were recovered, with a solids content of 0.68% and a calcium 
content in the solids of 29.2%. 
(EXAMPLE 7) 42.0 mL (50.0 g) of 37.4% HCl was added to 458 mL of water, and 
the resulting 500 mL of 3.1% (v/v) or 3.7% (w/w) HCl was added to 250 g of 
the wet sludge (taking into account water content in the sludge, the final 
concentration of HCl in the liquid was 2.6% v/v, or 3.0% w/w). The mixture 
was agitated with a propeller mixer for 30 min. 400 mL of liquid was 
collected. The liquid contained 5.8% of solids (dried at 105.degree. C.). 
Elemental calcium content in the dried solids was determined to be 29.8%, 
translating into 83% CaCl, or 110% CaCl.sub.2.2H.sub.2 O relative to the 
total solids. 
Combustion of the dried solids at 525.degree. C. reduced their weight by 
17.5% (the theoretical value for transition of CaCl.sub.2.2H.sub.2 O into 
CaCl.sub.2 is 24.5%), and the calcium content in the combusted solids was 
determined to be 33.0%, translating into 92% CaCl.sub.2 relative to the 
total solids. 
111.8 g of the unwashed and dried sludge residue was collected, with an 
average calcium content 7.0%. Washing of the residue with a 5-fold excess 
of water resulted in 98% recovery of the solid residue and 96% recovery of 
the wash waters. Elemental calcium content of the washed solid residue, 
dried at 105.degree. C., was determined to be 4.2%. Drying of the wash 
waters at 105.degree. C. resulted in solids (0.49% by weight) with a 
calcium content of 29.1%, translating into 81% CaCl.sub.2, or 107% 
CaCl.sub.2.2H.sub.2 O. 
EXAMPLES 8 THROUGH 10 
The procedure of Example 7 was repeated, but with the difference that the 
reaction time was 5 min and 15 min. The example with the reaction time 30 
min was also repeated. The data obtained are listed in the following Table 
3. 
TABLE 3 
______________________________________ 
Solubilization of calcium from mixed office paper sludge with HCl (in 
an amount equal to 0.8 times the stoichiometric amount of calcium 
carbonate in the sludge) 
Weight loss 
Solids after 
CaCl.sub.2 in 
at CaCl.sub.2 in the 
EXAM- Time, extraction, 
dried solids, 
combustion, 
combusted 
PLE min % % % solids, % 
______________________________________ 
8 5 5.0 60 23 89 
9 15 5.3 65 27 91 
10 30 4.7 86 24 93 
______________________________________ 
It is apparent that an increase in reaction time from 5 min to 15 min. and 
further to 30 min, results in a higher purity of the target calcium 
chloride. This is probably due to the slower solubilization of calcium 
compared with other components of the sludge that are also solubilized by 
HCl. 
EXAMPLES 11 AND 12 
The procedure of Example 3 was repeated, but with the difference that the 
reaction time was 5 min and then 15 min. The data obtained are listed in 
the following Table 4 together with those of Example 3. 
TABLE 4 
______________________________________ 
Solubilization of calcium from mixed office paper sludge with HCl (in 
an amount equal to 1.2 times the stoichiometric amount of calcium 
carbonate in the sludge) 
Weight loss 
Solids after 
CaCl.sub.2 in 
at CaCl.sub.2 in the 
EXAM- Time, extraction, 
dried solids, 
combustion, 
combusted 
PLE min % % % solids, % 
______________________________________ 
11 5 8.9 64 21 63 
12 15 8.4 57 16 83 
3 30 8.2 73 18 93 
______________________________________ 
As was also shown in Examples 7 through 10, it is apparent that an increase 
in reaction time from 5 min to 15 min, and further to 30 min, results in a 
higher purity of the target calcium chloride. It is also apparent from the 
data in Tables 3 and 4 that a higher purity of the material combusted at 
525.degree. C. (last column in both tables) results from a loss of 16% to 
27% of volatile solids (bound water and other combustible compounds). 
EXAMPLES 13 THROUGH 23 
The procedure of Examples 3, 5, and 7 were repeated (for stoichiometric 
ratios of HCl to CaCO.sub.3 in the sludge equal to 1.2, 1.0, and 0.8), but 
with the difference that the reaction time was 60 min and then 120 min. 
The data obtained are listed in the following tables 5-8 together with the 
data of Examples 3, 5, and 7-12. 
(EXAMPLE 13) The stoichiomctric ratio was 0.8 and the reaction time was 30 
min. 
(EXAMPLE 14) The stoichiometric ratio was 0.8 and the reaction time was 60 
min. 
(EXAMPLE 15) The stoichiometric ratio was 0.8 and the reaction time was 120 
min. 
(EXAMPLE 16) The stoichiometric ratio was 1.0 and the reaction time was 5 
min. 
(EXAMPLE 17) The stoichiometric ratio was 1.0 and the reaction time was 15 
min. 
(EXAMPLE 18) The stoichiometric ratio was 1.0 and the reaction time was 30 
min. 
(EXAMPLE 19) The stoichiometric ratio was 1.0 and the reaction time was 60 
min. 
(EXAMPLE 20) The stoichiometric ratio was 1.0 and the reaction time was 120 
min. 
(EXAMPLE 21) The stoichiometric ratio was 1.0 and the reaction time was 30 
min. 
(EXAMPLE 22) The stoichiometric ratio was 1.2 and the reaction time was 60 
min. 
(EXAMPLE 23) The stoichiometric ratio was 1.2 and the reaction time was 120 
min. 
TABLE 5 
______________________________________ 
Solubilization of calcium from mixed office paper sludge with HCl. 
The concentration of extractable solids is shown for different 
stoichiometric proportions of the acid relative to calcium carbonate 
content in the sludge, and for different reaction times 
Stoichiometric ratio of HCl to CaCO.sub.3 in 
Average 
the sludge concentration, 
Time, min 
0.8 1.0 1.2 % 
______________________________________ 
5 5.0 6.3 8.9 6.7 .+-. 2.0 
15 5.3 6.4 8.4 6.7 .+-. 1.6 
30 5.1 .+-. 0.6 
5.8 .+-. 0.2 
7.6 .+-. 0.5 
6.2 .+-. 1.3 
60 4.6 5.9 7.3 5.9 .+-. 1.4 
120 4.9 5.7 7.1 5.9 .+-. 1.1 
Average 5.0 .+-. 0.3 
6.0 .+-. 0.3 
7.8 .+-. 0.8 
concentration, 
______________________________________ 
TABLE 6 
______________________________________ 
Solubilization of calcium from mixed office paper sludge with HCl. 
The fraction of CaCl.sub.2 (anhydrous) in the extracted solids, 
dried at 105.degree. C., is shown for different stoichiometric 
proportions of the acid relative to calcium carbonate in the sludge, 
and for different reaction times 
Stoichiometric ratio of HCl to CaCO.sub.3 in 
the sludge Average CaCl.sub.2 
Time, min 
0.8 1.0 1.2 fraction, % 
______________________________________ 
5 60 77 64 67 .+-. 9 
15 65 76 57 66 .+-. 10 
30 84 .+-. 2 82 .+-. 2 
77 .+-. 4 
81 .+-. 5 
60 88 87 84 86 .+-. 2 
120 80 81 84 82 .+-. 2 
Average 77 .+-. 12 
81 .+-. 4 
74 .+-. 11 
77 .+-. 10 
CaCl.sub.2 
fraction, % 
______________________________________ 
TABLE 7 
______________________________________ 
Solubilization of calcium from mixed office paper sludge with HCl. 
Weight loss reflects drying of solids at 105.degree. C., folloiwng 
combustion 
at 525.degree. C. The data are shown for the different stoichiometric 
proportions of the acid relative to calcium carbonate in the sludge, and 
for different reaction times 
Stoichiometric ratio of HCl to CaCO.sub.3 in 
the sludge Average weight 
Time, min 
0.8 1.0 1.2 loss, % 
______________________________________ 
5 23 n.d. 21 22 .+-. 2 
15 27 n.d. 16 22 .+-. 7 
30 17 .+-. 6 
13 .+-. 2 15 .+-. 3 
15 .+-. 5 
60 8 9 13 10 .+-. 3 
120 11 19 17 16 .+-. 4 
Average 17 .+-. 8 
13 .+-. 4 16 .+-. 3 
16 .+-. 7 
weight loss, % 
______________________________________ 
TABLE 8 
______________________________________ 
Solubilization of calcium from mixed office paper sludge with HCl. 
The fraction of CaCl.sub.2 (anhydrous) in the solids, combusted at 
525.degree. C., is shown for different stoichiometric proportions of 
the acid, and for different reaction times 
Stoichiometric ratio of HCl to CaCO.sub.3 in 
the sludge Average CaCl.sub.2 
Time, min 
0.8 1.0 1.2 fraction, % 
______________________________________ 
5 89.1 n.d. 62.7 76 .+-. 19 
15 91.0 n.d. 83.3 87 .+-. 5 
30 91.4 .+-. 0.2 
90.0 .+-. 1.3 
88.8 .+-. 4.4 
90 .+-. 3 
60 91.3 93.5 84.9 90 .+-. 4 
120 92.1 89.4 87.4 90 .+-. 2 
______________________________________ 
It apparent from Tables 5-8 that: 
The concentration of the extracted solids generally increased with 
increasing HCl concentration in the reaction mixture, 
The fraction of CaCl.sub.2 in the extracted solids (dried at 105.degree. 
C.), calculated as the anhydrous salt, does not depend noticeably on the 
amount of HCl in the reaction mixture (at least in the range tested) and 
on the reaction time, and is equal to 77.+-.10%, 
When combusted at 525.degree. C., the extracted solids lose 16.+-.7% of 
their weight, apparently in the form of bound water (since they contain 
only a small amount of organic materials, as Tables 1 and 2 show), 
The fraction of CaCl.sub.2 in the combusted solids increases with 
decreasing amounts of HCl in the reaction system, reaching 91%-92% at a 
stoichiometric proportion of HCl to CaCO.sub.3 in the reaction system 
equal to 0.8, and 
During the initial period of the reaction (the first 5 to 15 min in the 
conditions described) the fraction of CaCl.sub.2 was rather low, and 
reached 91%-92% at 30-60-120 min. 
In EXAMPLE 15, after 120 min of reaction with a stoichiometric amount of 
HCl equal to 0.8, 405 mL of the extract was recovered along with 93.5 g of 
dry unwashed solid residue, with elemental calcium content 6.2%. After the 
residue was washed and dried, it contained 5.4% calcium. The solids 
recovered from the wash waters and dried at 105.degree. C. contained 27.4% 
elemental calcium, translating into 76% CaCl.sub.2 content. Combustion of 
these solids at 525.degree. C. increased the calcium content to 31.6%, 
that is, 87.7% CaCl.sub.2. 
In EXAMPLE 20, after 120 min of reaction with the stoichiometrically 
equivalent amount of HCl, 425 mL of the extract was recovered along with 
104 g of dry unwashed solid residue, with an elemental calcium content of 
7.8%. After the residue was washed and dried, it contained 2.1% calcium. 
The solids recovered from the wash waters and dried at 105.degree. C. 
contained 29.1% elemental calcium, translating into 81% CaCl.sub.2 
content. Combustion of these solids at 525.degree. C. increased the 
calcium content to 33.1%, that is, 91.9% CaCl.sub.2. 
In EXAMPLE 23, after 120 min of reaction with a stoichiometric proportion 
of HCl equal to 1.2, 385 mL of the extract was recovered along with 112 g 
of dry unwashed solid residue, with an elemental calcium content of 5.0%. 
After the residue was washed and dried, it contained 1.9% calcium. The 
solids recovered from the wash waters and dried at 105.degree. C. 
contained 27.2% elemental calcium, translating into 75.5% CaCl.sub.2 
content. Combustion of these solids at 525.degree. C. increased the 
calcium content to 33.7%, that is 93.5% CaCl.sub.2. 
EXAMPLE 24 
The procedure of Example 1 was repeated, but with the difference that the 
amount of HCl added to the sludge was 2.05 times stoichiometric amount of 
calcium carbonate in the sludge, and the total amount of the diluted HCl 
added (as well as the conditions of the reaction) differed from Example 1. 
82 mL of 20% (v/v) HCl (23.8% w/w) was added to 100 g of the wet sludge 
(taking into account water content in the sludge, the HCl concentration in 
the reaction system was 13.1% v/v), agitated, and incubated overnight at 
room temperature. Then 82 mL of water were added, making the final HCl 
concentration 7.9% (v/v) or 9.1% (w/w). 96 mL of the resulting liquid was 
collected, and this determined to contain 15.0.+-.0.3% solids (based on an 
average of two separate drying procedures at 105.degree. C.). Elemental 
calcium content in the dried solids was 12.6%, translating into 35% CaCl, 
or 46% CaCl.sub.2.2H.sub.2 O relative to total solids. 
Combustion of the dried solids at 525.degree. C. reduced their weight by 
41% (the theoretical value for transition of CaCl.sub.2.2H.sub.2 O into 
CaCl.sub.2 is 24.5%), and the calcium content in the combusted solids was 
24.4%, translating into 68% CaCl.sub.2. 
38.3 g of the washed and dried sludge residue was collected. The calcium 
content in the residue was 1.2%. 
EXAMPLE 25 
The procedure of Example 24 was repeated, but with a different order of 
mixing the reagents and separating the resulting liquid from the residual 
solids. 82 mL of 20% (v/v) HCl was first diluted with 82 mL of water, and 
then the resulting 10% (v/v) HCl was added to 100 g of the wet sludge. The 
final concentration of the reagents in the reaction mixture was the same 
as in Example 23. After overnight incubation the supernatant was decanted, 
and the collected insoluble sludge residue placed into a Buchner funnel 
and subjected to vacuum filtration using house vacuum. 132 mL total of the 
liquid was collected and filtered through Whatman No. 1 filter paper. 
Solids content in the collected liquid was 12.0%, as shown by evaporation 
of a 10-mL sample at 105.degree. C. Combustion of the dried solids at 
525.degree. C. reduced their weight by 43.5% (the theoretical value for 
transition of CaCl.sub.2.2H.sub.2 O into CaCl.sub.2 is 24.5%). 35.8 g of 
the washed and dried sludge residue was collected. 
EXAMPLES 26 THROUGH 29 
The procedures of Examples 8 through 10 and 14 were repeated, but with the 
difference that the initial material was fines and minerals separated from 
mixed office sludge, and the amount of the material was 317 g. This 
material had a moisture content 56.9%, an elemental calcium content of 
12.04% (dry matter), giving a calcium carbonate content of 30.1% in the 
whole dried sludge. 52 mL (61.9 g) of 37.4% HCl was added to 448 mL of 
water, and the resulting 500 mL of 3.9% (v/v) or 4.5% (w/w) HCl was added 
to 317 g of the wet sludge (taking into account water content in the 
sludge, the final concentration of HCl in the liquid was 2.9% v/v, or 3.4% 
w/w). That stoichiometric proportion of HCl was 0.8 relative to a complete 
solubilization of the calcium carbonate present in the initial material 
(41.1 g of calcium carbonate require 80.2 g, or 67.4 mL, of 37.4% HCl). 
The mixture was agitated with a propeller mixer. The data obtained are 
listed in Table 9. 
TABLE 9 
______________________________________ 
Solubilization of calcium from fines and minerals (obtained from 
mixed office paper sludge) with HCl (stoichiometric proportion 
of 0.8 relative to calcium carbonate content in the sludge) 
Weight loss 
Solids after 
CaCl.sub.2 in 
at CaCl.sub.2 in the 
EXAM- Time, extraction, 
dried solids, 
combustion, 
combusted 
PLE min % % % solids, % 
______________________________________ 
26 5 5.9 72 24 96 
27 15 5.9 72 28 93 
28 30 6.1 76 31 92 
29 60 6.6 76 25 92 
Average 6.1 .+-. 0.3 
74 .+-. 2 
27 .+-. 3 
93 .+-. 2 
______________________________________ 
As in Examples 7 through 12, it is apparent that an increase in reaction 
time (up to 30-60 min) generally results in a higher purity of the target 
calcium chloride, probably because of the slower solubilization of calcium 
compared with other components of the sludge that are also solubilized by 
HCl. 
EXAMPLES 30 THROUGH 33 
The procedures of Examples 26 through 29 were repeated, but with the 
difference that the amount of HCl was stoichiometrically equivalent to 
calcium carbonate in the material (fines and minerals separated from mixed 
office sludge), and the amount of the material was 300 g. 63.5 mL (75.6 g) 
of 37.4% HCl was added to 436.5 mL of water, and the resulting 500 mL of 
4.7% (v/v) or 5.5% (w/w) HCl was added to 300 g of the wet sludge (taking 
into account water content in the sludge, the final concentration of HCl 
in the liquid was 3.5% v/v, or 4.1% w/w). That amount of HCl was the 
stoichiometric equivalent needed for complete solubilization of the 
calcium carbonate present in the initial material. The mixture was 
agitated with a propeller mixer. The data obtained are listed in the 
following Table 10. 
TABLE 10 
______________________________________ 
Solubilization of calcium from fines and minerals (obtained from 
mixed office paper sludge) with HCl stoichiometrically equivalent to 
calcium carbonate content in the sludge) 
Weight loss 
Solids after 
CaCl.sub.2 in 
at CaCl.sub.2 in the 
EXAM- Time, extraction, 
dried solids, 
combustion, 
combusted 
PLE min % % % solids, % 
______________________________________ 
30 5 6.5 70 33 91 
31 15 6.9 76 23 93 
32 30 6.6 85 23 94 
33 60 7.1 85 21 96 
Average 6.8 .+-. 0.3 
74 .+-. 2 
25 .+-. 5 
93 .+-. 2 
______________________________________ 
As in Examples 7 through 12, and 26 through 29, it is apparent that an 
increase in reaction time (up to 30-60 min) generally results in a higher 
purity of the target calcium chloride. 
EXAMPLE 34 
The procedure of Example 1 was repeated, but with the difference that 
diluted nitric acid was used for solubilization of calcium (in the form of 
calcium nitrate) from mixed office sludge from the same source as in 
Example 1, and of a similar composition. The initial sludge material had a 
moisture content of 38.4%, an ash content 31.5% (dry matter), and an 
elemental calcium content 8.16%, translating into a calcium carbonate 
content of 20.4% in the whole dry sludge. 150 mL of 20% nitric acid (143 
mL of 69.9% nitric acid diluted to 500 mL with water) was added to 100 g 
of the wet sludge. Taking into account water content in the sludge, the 
nitric acid concentration in the reaction system was 15.9% v/v, i.e., 1.9 
times the stoichiometric content of calcium carbonate content in the 
sludge. 90 mL of liquid was collected. The liquid contained 10.4.+-.0.2% 
of solids (based on an average of two separate experiments), as was shown 
by evaporation of a 10-mL sample at 105.degree. C. The theoretical 
concentration of calcium nitrate formed would be 10.9%. Elemental calcium 
content in the dried solids was 18.3.+-.0.5 (based on three separate 
measurements), translating into 75.+-.2% Ca(NO.sub.3).sub.2, or 108.+-.3% 
Ca(NO.sub.3).sub.2.4H.sub.2 O. 
41.6 g of the washed and dried sludge residue was collected. 
EXAMPLE 35 
The procedure of Example 34 was repeated, but with the difference that 200 
mL of 20% nitric acid was used for solubilization of calcium, representing 
2.53 times the stoichiometric content of calcium carbonate in the sludge. 
200 mL of 20% nitric acid (143 mL of 69.9% nitric acid diluted to 500 mL 
with water) was added to 100 g of the wet sludge. Taking into account 
water content in the sludge, the nitric acid concentration in the reaction 
system was 16.8% v/v. 130 mL of liquid was collected. The liquid contained 
8.6% solids as was shown by evaporation of a 10-mL sample at 105.degree. 
C. The theoretical concentration of calcium nitrate formed would be 8.6%. 
Elemental calcium content in the dried solids was 18.7.+-.1.4 (based on 
three separate measurements), translating into 776% Ca(NO.sub.3).sub.2, or 
110.+-.8% Ca(NO.sub.3).sub.2.4H.sub.2 O. 
41.4 g of the washed and dried sludge residue was collected. 
EXAMPLE 36 
The procedure of Example 34 was repeated, but with the difference that 
diluted acetic acid was used for solubilization of calcium (in the form of 
calcium acetate) from mixed office sludge. 150 mL of 20% acetic acid was 
added to 100 g of the wet sludge. Taking into account water content in the 
sludge, the acetic acid concentration in the reaction system was 15.9% 
v/v, representing 2.0 times the stoichiometric content of calcium 
carbonate in the sludge. 88 mL of liquid was collected. The liquid 
contained 10.2% solids, as was shown by evaporation of a 10-mL sample at 
105.degree. C. The theoretical concentration of calcium acetate formed 
would be 10.6%. Elemental calcium content in the dried solids was 
21.8.+-.0.2 (based on three separate measurements), translating into 
86.+-.1% Ca(CH.sub.3 COO).sub.2, or 96.+-.1% Ca(CH.sub.3 
COO).sub.2.H.sub.2 O. 
40.3 g of the washed and dried sludge residue was collected. 
EXAMPLE 37 
The procedure of Example 36 was repeated, but with the difference that 200 
mL of 20% acetic acid was used for solubilization of calcium, representing 
2.66 times the stoichiometric content of calcium carbonate in the sludge. 
200 mL of 20% acetic acid was added to 100 g of the wet sludge. Taking 
into account water content in the sludge, the acetic acid concentration in 
the reaction system was 16.8% v/v. 130 mL, of liquid was collected. The 
liquid contained 8.0% of solids as was shown by evaporation of a 10-mL 
sample at 105.degree. C. The theoretical concentration of calcium acetate 
formed would be 8.3%. The elemental calcium content in the dried solids 
was 21.2.+-.0.1 (based on three separate measurements), translating into 
84.+-.1% Ca(CH.sub.3 COO).sub.2, or 93.+-.1% Ca(CH.sub.3 
COO).sub.2.H.sub.2 O. 
42.3 g of the washed and dried sludge residue was collected. 
EXAMPLE 38 
The procedure of Example 36 was repeated, but with the difference that 4.0 
kg of wet mixed office sludge (48.2% moisture, calcium carbonate content 
of 20.4% in the dry sludge) was treated with 7.2 L of 11.6% acetic acid, 
representing 1.7 times the stoichiometric content of calcium carbonate 
content in the sludge. 
The solubilization was performed as follows. 829 mL (870 g) of glacial 
acetic acid was mixed with 6,316 mL of tap water, making 7,145 mL of 11.6% 
(v/v) or 12.2% (w/w) acetic acid. This was added to 4.0 kg of the wet 
sludge at room temperature. Taking into account the amount of water in the 
sludge, the concentration of acetic acid in the resulting liquid was 9.1% 
(v/v) or 9.6% (w/w). The mixture was left for three days, after which 
supernatant was decanted, and 4.8 L of liquid was collected using a large 
Buchner funnel subjected to vacuum filtration using house vacuum. The pH 
of the liquid was 4.9. The solids content was 9.91%, as shown by 
evaporation of a 10-mL sample at 105.degree. C. The theoretical amount of 
calcium acetate, formed in the reaction mixture, would have been 7.4% 
(anhydrous) or 8.2% (monohydrate) by weight. The elemental calcium content 
in the solids was 21.9%, translating into 86.5% calcium acetate 
(anhydrous), or 96.4% calcium acetate dihydrate. 
EXAMPLE 39 
The procedure of Example 38 was repeated, but with the difference that 5.0 
kg of wet mixed office sludge (46.6% moisture, calcium carbonate content 
21.1% in the dry sludge) was treated with 644 mL (676 g) of glacial acetic 
acid (diluted to 5.93 L with water and resulted in 10.85% acetic acid, 
v/v). This amount of acetic acid was stoichiometrically equivalent to the 
calcium carbonate in the sludge. Taking into account water content in the 
sludge, the acetic acid concentration in the reaction mixture liquid was 
7.8% (v/v), or 8.1% (w/w). 
The solubilization was performed for 4 hours at room temperature, and 5 L 
of liquid was collected under press. After 45 min of reaction, the 
elemental calcium content in a sample of the washed and dried solid 
residue was 2.0% (5% of calcium carbonate); after 4 hours, the solid 
residue contained 0.5% of elemental calcium, translating into 1.25% 
calcium carbonate. 
Solids content in the obtained extract was 9.2%, as shown by evaporation of 
a 5-mL sample at 105.degree. C. The theoretical amount of calcium acetate, 
formed in the reaction mixture, would have been 10.8% (anhydrous) by 
weight. The elemental calcium content in the solids was 22.3%, translating 
into 88.1% calcium acetate anhydrous, or 98.1% calcium acetate 
monohydrate. 
When the dried solids were heated at 525.degree. C., 44.3% of the weight 
loss was observed. That corresponded to the loss of one water molecule and 
one acetone molecule by calcium acetate (the theoretical weight loss is 
43.2%). The resulting material contained 40.2% of calcium, corresponding 
to practically pure calcium carbonate (theoretical calcium content is 
40.0%). Hence, the acetic acid extract contained practically pure calcium 
acetate monohydrate. 
EXAMPLE 40 
The procedure of Example 39 was repeated, but with a different sample of 
mixed office sludge (although similar in composition to the sample of 
Example 39), and with a smaller volume of diluted acetic acid added. The 
calcium carbonate content was 24.0%, and the moisture content 47.1%. 5 kg 
of the material was treated with 726 mL (762 g) of glacial acetic acid 
(diluted to 4.33 L with water, resulting in 16.8% acetic acid, v/v). This 
amount of acetic acid was stoichiometrically equivalent to the calcium 
carbonate in the sludge. Taking into account water content in the sludge, 
the acetic acid concentration in the reaction mixture liquid was 10.9% 
(v/v), or 11.3% (w/w). 
The solubilization was performed for 3 hours at room temperature, and 2.9 L 
of liquid was collected under press. The solids content was 13.7%, as 
shown by evaporation of a 5-mL sample at 105.degree. C. The theoretical 
amount of calcium acetate formed in the reaction mixture would have been 
15% (anhydrous) by weight. Elemental calcium content in the solids was 
determined to be 20.4%, translating into 80.6% of calcium acetate 
anhydrous, or 89.8% calcium acetate monohydrate. 
When the dried solids were heated at 525.degree. C., 43.4% of the weight 
loss was observed. That corresponded to the loss of one water molecule and 
one acetone molecule by calcium acetate (the theoretical weight loss is 
43.2%). The resulting material contained 39.6% of calcium, corresponding 
to practically pure calcium carbonate (theoretical calcium content is 
40.0%). Hence, the acetic acid extract contained practically pure calcium 
acetate monohydrate. 
EXAMPLE 41 
This example describes solubilization of calcium by acetic acid (in the 
form of calcium acetate) from dried mixed office sludge. The initial 
sludge material was dried, dust-free, not screened, and had a moisture 
content of 3.9%, an ash content 60%, and an elemental calcium content of 
5.4%, resulting in a calcium carbonate content of 13.5% in the whole dried 
sludge. 
The solubilization was performed as follows. 300 g of the dried sludge was 
added by portions of 80-120 g into 625 mL of 20% acetic acid (prepared by 
mixing 125 mL of glacial acetic acid and 500 mL of tap water) at room 
temperature. The acetic acid concentration in the reaction system was 2.6 
times the stoichiometric proportion of calcium carbonate in the sludge. A 
moderate evolution of carbon dioxide was observed. The mixture was left 
overnight, following which supernatant was decanted, and 310 mL of the 
brownish liquid was then collected. The solids content was 15.7%, as was 
shown by evaporation of a 10-mL sample at 105.degree. C. The elemental 
calcium content in the liquid was 28,250 ppm, translating into 11.2% 
calcium acetate. 
Complete solubilization of calcium carbonate (13.5% in the sludge, as noted 
above, or 40.5 g in 300 g of the sludge) would theoretically yield 64 g of 
calcium acetate in 625 mL total solution, i.e., 10.2%. This figure can be 
compared with the 11.2% concentration of calcium acetate determined 
experimentally. 
The washed and dried sludge residue (after the acid extraction) included 
49% ash, compared with 60% ash content in the initial sludge material. 
EXAMPLE 42 
The procedure of Example 41 was repeated, but with the difference that 3.84 
kg of the dried sludge was added by batches of 100-200 g into 8 L of 20% 
acetic acid (prepared by mixing of 1.6 L of glacial acetic acid and 6.4 L 
of tap water). The acetic acid concentration in the reaction system was 
2.6 times the stoichiometric proportion of calcium carbonate in the 
sludge. After overnight incubation the supernatant was decanted, and the 
collected insoluble sludge residue placed into a large Buchner funnel and 
subjected to vacuum filtration using house vacuum. 3.9 L total of the 
liquid, pH 4.4, was collected. The liquid was filtered through Whatman No. 
1 filter paper, resulting in a brownish clear solution with solids content 
of 15.4% (shown by evaporation of a 10-mL sample at 105.degree. C.). The 
calcium content in the liquid was 23,000 ppm, translating into 9.1% 
calcium acetate. 
Complete solubilization of calcium carbonate (13.5% in the sludge, see 
Example 41, or 518.4 g in 3.84 kg of the sludge) would theoretically yield 
819.07 g of calcium acetate in 8 L of total solution, that is 10.2%. This 
figure can be compared to the 9.1% concentration of calcium acetate 
determined experimentally. 
EXAMPLE 43 
The procedure of Example 41 was repeated, but with the difference that 
another, high-ash sludge material was treated with 20% acetic acid. The 
sludge material was dried, dust-containing, with a moisture content of 5%, 
an ash content of 63%, and an elemental calcium content of 17.2%, 
translating into a calcium carbonate content of 43%. 
171.2 g of the dried sludge was added carefully into 625 mL of 20% acetic 
acid (prepared by mixing of 125 mL of glacial acetic acid and 500 mL of 
tap water) at room temperature. The acetic acid concentration in the 
reaction system was 1.5 times the stoichiometric proportion of calcium 
carbonate in the sludge. A violent evolution of carbon dioxide was 
observed, forming a thick "beer head." The mixture was left overnight to 
ensure completion of the reaction. Supernatant was then separated by a 
multiple stepwise decanting, since the dusty, insoluble sludge residue did 
not allow a clean direct decanting. 300 mL of turbid liquid was collected 
over a 24-hr period. After filtration, the solids content in the liquid 
was observed to be 18.7%, as shown by evaporation of a 10-mL sample at 
105.degree. C. 
Complete solubilization of calcium carbonate in the sludge (73.6 g in 171.2 
g of the sludge) would theoretically yield 116.3 g of calcium acetate in 
625 mL of total solution, i.e., 18.6%, practically identical to the 18.7% 
concentration of solids determined experimentally. 
EXAMPLE 44 
This example describes solubilization of calcium (in the form of calcium 
chloride) from yet another mixed office sludge, combusted under controlled 
conditions, namely at 525.degree. C. The dry ash contained 24.9% elemental 
calcium, translating into 62.3% calcium carbonate. The solubilization was 
performed by diluted HCl, in amount of 1.3 times the stoichiometric 
proportion of calcium carbonate content. 
The solubilization was performed as follows. 500 mL of 11.9% (w/w) of HCl, 
prepared by diluting 535 mL (636.65 g) of 37.4% HCl to 2 L, was added to 
100 g of the dry ash. That amount of HCl was 31% higher than the 
stoichiometric amount needed for a complete solubilization of the calcium 
carbonate present in the ash. The mixture was agitated and left overnight 
at room temperature. Supernatant was then separated from the solid residue 
by decanting and filtering, and 243 mL of liquid was collected. The liquid 
contained 15.8% of solids, as was shown by evaporation of a 10-mL sample 
at 105.degree. C. The elemental calcium content in the dried solids was 
27.6%, translating into 77% CaCl, or 101% CaCl.sub.2.2H.sub.2 O. 
Combustion of the dried solids at 525.degree. C. reduced their weight by 
24.7% (the theoretical value for transition of CaCl.sub.2.2H.sub.2 O into 
CaCl.sub.2 is 24.5%), and the elemental calcium content in the combusted 
solids was 29%, translating into 80% CaCl.sub.2 in the total solids. 48.5 
g of the washed and dried sludge residue was collected. Elemental calcium 
content in the residue was determined to be 3.3%. The material contained 
primarily clay. 
EXAMPLE 45 
The procedure of Example 44 was repeated, but with the difference that the 
ash, treated with diluted HCl, was obtained by combustion at 900.degree. 
C. The dry ash contained 30.0.+-.0.4% elemental calcium, translating into 
42.0.+-.0.6% calcium oxide equivalent. The amount of HCl, used for the 
solubilization, was 1.09 times the stoichiometric proportion of calcium 
carbonate in the ash. 
The solubilization was performed as follows. 170 mL of 11.9% (w/w) HCl, 
prepared as described in Example 44, was added to 34 g of the dry ash. 
That amount of HCl was 9% higher compared with the stoichiometric amount 
needed for complete solubilization of calcium carbonate present in the 
ash. The mixture was agitated and left overnight at room temperature. 
Supernatant was then separated from the solid residue by decanting and 
filtering, and 72 mL of liquid was collected. The liquid contained 18.8% 
solids, as shown by evaporation of a 10-mL sample at 105.degree. C. 
Elemental calcium content in the dried solids was 27.4%, translating into 
76% CaCl, or 100% CaCl.sub.2.2H.sub.2 O. 
Combustion of the dried solids at 525.degree. C. reduced their weight by 
25.5% (the theoretical value for transition of CaCl.sub.2.2H.sub.2 O into 
CaCl.sub.2 is 24.5%), and the elemental calcium content in the combusted 
solids was 32.3%, translating into 90% CaCl.sub.2 in the total solids. 24 
g of the washed and dried sludge residue was collected. Elemental calcium 
content in the residue was determined to be 7.8%. 
EXAMPLES 46 AND 47 
The procedure of Example 44 was repeated, but with the difference that 
diluted nitric acid was used for solubilization of calcium (in the form of 
calcium nitrate) from the ash obtained by combustion of the mixed office 
sludge at 525.degree. C. 200 g of the ash was mixed with 1.8 L of 20% 
nitric acid, prepared as in Example 35. That amount of nitric acid 
corresponded to 2.3 times the stoichiometric proportion of calcium 
carbonate in the ash. The slurry was agitated and left overnight at room 
temperature. The liquid collected was of a gel-like appearance and 
contained 18.5% of solids, as shown by evaporation of a 10-mL sample at 
105.degree. C. The elemental calcium content in the dried solids was 
13.75.+-.0.05% (based on two independent measurements), translating into 
56.4% Ca(NO.sub.3).sub.2, or 81.2% Ca(NO.sub.3).sub.2.4H.sub.2 O. 
In a similar experiment, 200 g of the ash was mixed with 3.0 L of 20% 
nitric acid, prepared as in Example 35. That amount of nitric acid 
corresponded to 3.8 times the stoichiometric proportion of calcium 
carbonate in the ash. The slurry was agitated and left overnight at room 
temperature. The liquid collected contained 11.0.+-.0.1% of solids (based 
on two separate measurements), as was shown by evaporation of a 10-mL 
sample at 105.degree. C. The elemental calcium content in the dried solids 
was 13.6.+-.0.1% (based on two independent measurements), translating into 
55.8% Ca(NO.sub.3).sub.2, or 80.3% Ca(NO.sub.3).sub.2.4H.sub.2 O. 
Combustion of the dried solids from both experiments at 525.degree. C. 
reduced their weight by 64% (the theoretical value for the transition of 
Ca(NO.sub.3).sub.2.4H.sub.2 O into anhydrous calcium carbonate is 57.6%). 
The calcium content in the combusted solids was determined to be 38.4%, 
corresponding to calcium carbonate of 96% purity. 
EXAMPLES 48 AND 49 
The procedure of Examples 46-47 was repeated, but with the difference that 
diluted acetic acid was used for solubilization of calcium (in the form of 
calcium acetate) from the ash obtained by combustion of the mixed office 
sludge at 525.degree. C. 200 g of the ash was mixed with 1.8 L of 20% 
(v/v) or 21% (w/w) acetic acid. That amount of acetic acid corresponded to 
2.5 times the stoichiometric proportion of calcium carbonate in the ash. 
The slurry was agitated and left overnight at room temperature. The liquid 
collected contained 14.0% solids, as shown by evaporation of a 10-mL 
sample at 105.degree. C. The theoretical amount of calcium acetate, formed 
in the reaction mixture, would have been 10.9% solids. The elemental 
calcium content in the dried solids was determined to be 19.6.+-.0.8% 
(based on four independent measurements), translating into 77% Ca(CH.sub.3 
COO).sub.2, or 86% Ca(CH.sub.3 COO).sub.2.H.sub.2 O. 
In a similar experiment, 200 g of the ash was mixed with 3.0 L of 20% (v/v) 
or 21% (w/w) acetic acid. That amount of acetic acid corresponded to 4.2 
times the stoichiometric proportion of calcium carbonate in the ash. The 
slurry was agitated and left overnight at room temperature. 2.7 L of 
liquid was collected. The liquid collected contained 9.2.+-.0.2% solids 
(based on two separate measurements), as was shown by evaporation of a 
10-mL sample at 105.degree. C. The theoretical amount of calcium acetate, 
formed in the reaction mixture, would have been 6.6% by weight. The 
elemental calcium content in the dried solids was determined to be 
19.2.+-.0.4% (based on two independent measurements), translating into 76% 
Ca(CH.sub.3 COO).sub.2, or 85% Ca(CH.sub.3 COO).sub.2.H.sub.2 O. 
Combustion of the dried solids from both experiments at 525.degree. C. 
reduced their weight by 53% (the theoretical value for the transition of 
Ca(CH.sub.3 COO).sub.2.H.sub.2 O into anhydrous calcium carbonate is 
43.2%, see Examples 39 and 40). The calcium content in the combusted 
solids was determined to be 39.2%, corresponding to 98% calcium carbonate. 
Since the initial ash did not contain organic matter, the last figure 
indicates that the acetic acid extract contained calcium acetate of 98% 
purity. 
EXAMPLES 50 THROUGH 57 
These examples describe and compare solubilization of calcium (in the form 
of calcium nitrate or calcium acetate) from mixed office sludge, combusted 
under controlled conditions, namely, at 525.degree. C., 800.degree. C., 
900.degree. C., and 1000.degree. C. The dry ash contained 24.9% elemental 
calcium, translating into 62.3% calcium carbonate or 34.9% calcium oxide 
equivalent. The solubilization was performed by treating of 1 g of the dry 
ash with 15 mL of 20% nitric acid or 20% acetic acid, in amounts 
corresponding to 3.8 and 4.0, respectively, times the stoichiometric 
proportion of calcium carbonate or calcium oxide equivalent (for calcined 
ash samples) in the sludge. The theoretical concentrations of 
Ca(NO.sub.3).sub.2 and Ca(NO.sub.3).sub.2.4H.sub.2 O, Ca(CH.sub.3 
COO).sub.2 and Ca(CH.sub.3 COO).sub.2.H.sub.2 O formed are, respectively, 
6.8% and 9.8%, 6.6% and 7.3%. 
The following table shows the experimental results in terms of the amount 
of solids extracted from the ash after the liquids collected were dried at 
105.degree. C. The average volume of the liquids collected was 12.0.+-.1.3 
mL for nitric acid solubilization, and 11.2.+-.1.2 mL for acetic acid 
solubilization. 
TABLE 11 
______________________________________ 
Concentration of solids extracted from ash obtained by combustion of 
mixed office sludge. 1 g of ash was treated with 15 mL of 20% acid 
in each experiment. Theoretical concentrations for the given 
experimental conditions: Ca(NO.sub.3).sub.2 -6.8%, Ca(NO.sub.3).sub.2.4H.s 
ub.2 O 
9.8%, Ca(CH.sub.3 COO).sub.2 -6.6%, Ca(CH.sub.3 COO).sub.2.H.sub.2 
O-7.3% 
Solids concentration in the extracts 
Combustion temperature, 
collected, % 
degrees Celcius 20% Nitric acid 
20% Acetic acid 
______________________________________ 
525 9.3 .+-. 0.4 
6.9 .+-. 0.1 
800 12.6 .+-. 0.6 
10.4 
900 12.9 11.2 
1000 8.1 8.8 
______________________________________ 
The treatment of calcined ash (at 800, 900, and 1000.degree. C.) with both 
20% nitric acid and 20% acetic acid resulted in formation of a yellow 
slimy gel-like mass that is rather difficult to separate from the extract. 
EXAMPLES 58 THROUGH 60 
These examples describe and compare the solubilization of calcium (in the 
form of calcium chloride, calcium nitrate or calcium acetate) from an 
industrial incineration ash. The moisture content in the ash was 32.3%. 
The dried ash contained 16.5% elemental calcium, translating into 23.1% 
calcium oxide equivalent. 
The solubilization was performed as in Example 44, but with the difference 
that hydrochloric, nitric, and acetic acids were used, and in amounts 
close to the stoichiometric equivalent of the calcium oxide in the ash. 
100 g of dry incineration ash was treated with the following acid 
solutions: 
(Example 58) 300 mL of 8.67% HCl, prepared by diluting of 225 mL (267.75 g) 
of 37.4% HCl to 500 mL with water, resulting in 20% w/w HCl, and by a 
further mixing of 130 mL of the 20% acid with 170 mL of water; 
(Example 59) 400 mL of 13% nitric acid, prepared by diluting of 143 mL of 
69.9% nitric acid to 500 mL with water, resulting in 20% HNO.sub.3, and by 
a further mixing of 260 mL of 20% nitric acid with 140 mL of water; and 
(Example 60) 400 mL of 13.1% acetic acid, prepared by diluting of 125 mL of 
glacial acetic acid to 625 mL with water, resulting in 21% (w/w) acetic 
acid, and by a further mixing of 250 mL of 21% nitric acid with 150 mL of 
water. 
In all the three examples the amounts of the acids were close to 
stoichiometric equivalents: 3% excess of the acid, no excess, and 6% 
excess, respectively. The amount of extract recovered was 200 mL (Example 
58), 210 mL (Example 59) and 270 mL (Example 60). The theoretical amount 
of solids (as anhydrous salts) in the extracts were: 15.3% for CaCl.sub.2, 
16.9% for Ca(NO.sub.3).sub.2, and 16.3% for Ca(CH.sub.3 COO).sub.2. 
Table 12 shows experimental results in terms of amount of solids extracted 
from the ash, after the liquids collected were dried at 105.degree. C. 
TABLE 12 
______________________________________ 
Concentration of solids extracted from an industrial incineration ash. 
100 g of ash was treated with approximately stoichiometric amounts 
of hydrochloric, nitric, and acetic acids. Theoretical concentrations 
for the given experimental conditions: CaCl.sub.2 -15.3% (Ca content 
36.0%), CaCl.sub.2.2H.sub.2 O-20.2% (Ca content 27.2%), 
Ca(NO.sub.3).sub.2 -16.9% 
(Ca content 24.4%), Ca(NO.sub.3).sub.2.4H.sub.2 O-24.4% (Ca content 
16.9%), 
Ca(CH.sub.3 COO).sub.2 -16.3% (Ca content 25.3%), Ca(CH.sub.3 COO).sub.2.H 
.sub.2 O-18.1% 
(Ca content 22.7%) 
Solids Ca content 
concentration 
in solids, 
in the extracts, 
dried at Weight loss of 
Ca content in 
dried at 105.degree. C., 
solids at 525 
combusted 
Acid 105.degree. C. % 
% .degree.C., % 
solids, % 
______________________________________ 
Hydrochloric 
11.9 .+-. 1.3 
25.2 21.5 33.1 
Nitric 23.7 .+-. 0.5 
21.7 52.4 40.3 
Acetic 10.5 .+-. 1.1 
25.7 46.7 36.1 
______________________________________ 
It is apparent that acid-extracted chlorides, nitrates, and acetates, dried 
at 105.degree. C., contained a high fraction of components, volatile at 
525.degree. C. and/or decomposed at that temperature. In the case of 
calcium chloride, combustion eliminates bound water. Calcium nitrate 
converts to practically pure calcium carbonate (the theoretical calcium 
content is 40%, compared to 40.3% in Table 12). Calcium acetate loses a 
water molecule and an acetone molecule (the theoretical weight loss is 
42.3%) and converts to calcium carbonate (the theoretical calcium content 
is 40%, compared to 36.1% in Table 12, corresponds to CaCO.sub.3 of 90.3% 
purity). 
EXAMPLES 61 THROUGH 63 
This example describes precipitation of calcium carbonate from calcium 
chloride solutions obtained by processing of the mixed office sludge 
(Example 25), and ash residues after combustion of the sludge at 
525.degree. C. (Example 44) and 900.degree. C. (Example 45). 
The precipitation was performed by adding solutions of potassium carbonate, 
potassium bicarbonate, or sodium carbonate either to the calcium chloride 
solutions directly, or to the calcium chloride solutions diluted 4- to 
20-fold. The addition of potassium carbonate to the calcium chloride 
solutions (with no dilution) caused an almost immediate hardening of the 
solution due to the instant formation of calcium carbonate. When the 
calcium chloride solution is diluted 20-fold, addition of 1-5% v/v of the 
potassium carbonate solution leads to a fast formation of flakes of 
precipitated calcium carbonate. Microphotographs showed that the 
precipitated calcium carbonate formed right spheres of 1-2 microns in 
diameter (for some particular cases), with the size and shape of particles 
depending upon precipitation conditions. 
Table 13 shows the results of precipitating calcium carbonate by adding 
potassium carbonate (0.67 mg/mL) into the calcium chloride solutions. 10 
mL each of the calcium-containing extracts, obtained in Examples 25, 44, 
and 45, were diluted to 40 mL, 3 mL of the potassium carbonate solution 
was added, precipitate was collected by centrifugation, dried at 
105.degree. C. and weighed, and elemental calcium content was determined. 
The supernatant was mixed with another 3 mL of potassium carbonate 
solution, and the precipitate was collected, dried, and analyzed as 
described above. In a separate experiment, 12 mL of potassium carbonate 
was added into 40 mL of diluted calcium-containing extract, as described 
above. 
TABLE 13 
______________________________________ 
Precipitation of calcium-containing carbonates from calcium 
chloride-containing extracts obtained from mixed office sludge 
and calcined sludge (Examples 25, 44, 45) 
Precipitate, at 105.degree. C. 
K.sub.2 CO.sub.3 
Carbo- Precipitate, at 525.degree. C. 
Initial 
added, nates, Ca, CaCO.sub.3 
Weight 
Ca, CaCO.sub.3 
material 
mL mg % % loss, % 
% % 
______________________________________ 
Sludge 3 264 35.0 88 7.8 .+-. 
37.7 94 
0.2 
+3 289 34.7 87 5.1 .+-. 
36.5 91 
0.8 
12 1,261 35.3 88 5.5 37.4 94 
Ash, 525 
3 661 32.8 82 6.1 32.4 81 
.degree.C. 
+3 542 37.2 93 4.2 37.3 93 
12 1,359 33.7 84 6.6 34.7 87 
Ash, 900 
3 901 38.4 96 1.5 38.0 95 
.degree.C. 
+3 767 38.0 95 1.0 38.1 95 
12 1,913 33.4 84 8.0 35.8 90 
______________________________________ 
The data show that the calcium carbonate content in the dried precipitate 
before and after its combustion at 525.degree. C. was 88.+-.1% and 
93.+-.2%, respectively (from sludge), 86.+-.6% and 87.+-.6% (from ash at 
525.degree. C.), and 92.+-.7% and 93.+-.3% (from ash at 900.degree. C.). 
It is apparent that the precipitated calcium carbonate does not contain 
bound water, and its purity is in the neighborhood of 93%. 
EXAMPLE 64 
The procedure of Examples 61-63 was repeated, but with the difference that 
calcium carbonate was precipitated from the combined calcium nitrate 
solutions obtained in Examples 46 and 47. The mixed office sludge, 
combusted at 525.degree. C., was used as the source of calcium, as 
described in those Examples. 
Table 14 shows the results of precipitating calcium carbonate by adding 
potassium carbonate (0.67 mg/mL) into the calcium nitrate solution. 10 mL 
of the calcium-containing extract was diluted to 40 mL, 3 mL of the 
potassium carbonate solution was added, precipitate was collected by 
centrifugation, dried at 105.degree. C. and weighed, and the elemental 
calcium content was determined. The supernatant was mixed with another 3 
mL of potassium carbonate solution, and the precipitate was collected, 
dried, and analyzed as described above. The second supernatant was mixed 
with 4 mL of potassium carbonate solution, and the precipitate was 
collected, dried, and analyzed as described above. 
TABLE 14 
______________________________________ 
Precipitation of calcium-containing carbonates from calcium 
nitrate-containing extracts obtained from mixed office sludge 
combusted at 525.degree. C. (Examples 46-47) 
K.sub.2 CO.sub.3 
Precipitate, at 105.degree. C. 
Precipitate, at 525.degree. C. 
added, CaCO.sub.3 CaCO.sub.3 
mL Ca, % % Ca, % % 
______________________________________ 
3 25.2 63 n.d. n.d. 
+3 23.8 60 33.2 83 
+4 27.7 69 35.2 88 
______________________________________ 
EXAMPLE 65 
The procedure of Example 64 was repeated, but with the difference that 
calcium carbonate was precipitated from combined calcium acetate 
solutions, obtained in Examples 48 and 49. The mixed office sludge, 
combusted at 525.degree. C., was used as the source of calcium, as 
described in those Examples. The data are shown in the following Table 15. 
TABLE 15 
______________________________________ 
Precipitation of calcium-containing carbonates from calcium 
acetate-containing extracts obtained from mixed office sludge 
combusted at 525.degree. C. (Examples 48-49) 
K.sub.2 CO.sub.3 
Precipitate, at 105.degree. C. 
Precipitate, at 525.degree. C. 
added, 
Carbonates, 
Ca, CaCO.sub.3 
Weight CaCO.sub.3 
mL mg % % loss, % 
Ca, % % 
______________________________________ 
3 100 25.5 64 n.d. 28.8 72 
+3 113 28.8 72 20.4 39.0 98 
+4 145 35.5 89 8.3 39.2 98 
______________________________________ 
EXAMPLE 66 
The procedure of Examples 61-63 was repeated, but with the difference that 
calcium carbonate was precipitated from the calcium chloride, calcium 
nitrate, and calcium acetate solutions, obtained in Examples 58 through 
60. The industrial incineration ash was used as the source of calcium, as 
described in those Examples. The data are shown in the following Table 16. 
TABLE 16 
__________________________________________________________________________ 
Precipitation of calcium-containing carbonates from calcium chloride-, 
calcium 
nitrate-, and calcium acetate-containing extracts obtained from 
industrial 
incineration ash (Examples 58-60) 
K.sub.2 CO.sub.3 
Precipitate, at 105.degree. C. 
Precipitate, at 525.degree. C. 
added, CaCO.sub.3 
Weight CaCO.sub.3 
Acid mL Carbonates, mg 
Ca, % 
% loss 
Ca, % 
% 
__________________________________________________________________________ 
HCl 3 little n.d. 
n.d. 
n.d. 
n.d. 
n.d. 
+3 875 33.7 
84 7.6 
36.3 
91 
12 932 36.4 
91 7.1 
38.2 
98 
HNO.sub.3 
3 457 n.d. 
n.d. 
n.d. 
n.d. 
n.d. 
+3 805 23.4 
59 18.7 
25.7 
64 
12 1,407 24.0 
60 17.3 
29.0 
73 
CH.sub.3 COOH 
3 473 25.8 
65 15.4 
31.3 
78 
+3 107 28.2 
71 n.d. 
n.d. 
n.d. 
12 702 26.5 
66 12.5 
31.1 
78 
__________________________________________________________________________ 
It is apparent that the purest calcium carbonate was obtained from calcium 
chloride (up to 98% purity in the combusted material), followed by that 
obtained from calcium acetate (78% purity), and by that obtained from 
calcium nitrate (up to 73% purity). 
It is also apparent that carbonates precipitated from nitrates and acetates 
contained significantly more combustible (at 525.degree. C.) components 
compared to carbonates precipitated from chlorides. Among those 
combustible components can be bound water, carbonates of some other 
elements, etc. 
EXAMPLE 67 
The procedure of Example 41 was repeated, but with the difference that 
after decanting of the obtained calcium acetate solution, residual 
insoluble sludge granules, impregnated with calcium acetate acidic 
solution, were collected, air-dried, and tested as a de-icer by means of a 
direct application onto ice. Ice cubes were taken from -20.degree. C. 
freezer, crushed in a blender, put into two identical 15-cm Petri dishes, 
and kept at -20.degree. C. for an hour to make the ice crush rock-solid. 
Then ice in one dish was covered with granules impregnated with calcium 
acetate, and both dishes (test and control) were placed in a freezer at 
-6.degree. C. Soon ice in the test dish started to release water, while 
ice in the control dish remained solid (no water was released). 
It is apparent that granules impregnated with calcium acetate show distinct 
de-icing properties. 
It will be apparent from the above that a new and unique process has been 
disclosed for the recovery of calcium salts from papermaking sludge. These 
salts are suitable for many uses, including preparation of reagent 
chemicals, such as calcium chloride, calcium nitrate, calcium acetate, and 
so forth, precipitation as calcium carbonate, preparation of liquid and 
solid de-icers, such as calcium acetate alone and in combination with 
known de-icing chemicals such as magnesium salts, preparation of 
sulfur-capturing sorbents based on calcium salts, etc. This process 
therefore provides new use for calcium-containing paper sludges that 
heretofore have primarily been burned or landfilled, creating 
environmental pressure. It will be clear from the present disclosure that 
calcium salts resulting from waste paper sludge in general may be utilized 
for a wide variety of purposes. 
Although this invention has been described in its preferred form and 
preferred practice with a certain degree of particularity, it is 
understood that the present disclosure of the preferred form and preferred 
practice has been made only by way of example and that numerous changes 
may be resorted to without departing from the spirit and the scope of the 
invention as hereinafter claimed.