Journal of Scientific Innovations for Development Volume 1(1), p. 54-63
www.novelpublications.com
ISSN: 2026-6553
CHEMICAL EXTRACTION OF HUMIC SUBSTANCES USING NATURAL
RESINS
1Ohene
1University
B. Apea* 2JamesH. Ephraim, and 1Okyere Isaac
for Development Studies, faculty of Applied Sciences, Applied Chemistry Department, Navrongo
Campus
2Catholic University College Fiapre, SunyaniBrongAhafo Region Ghana
ABSTRACT
Natural resources are a gift to any nation. The article focused on demonstrating that natural materials
hold the potential to generate income for any nation. The study tested the potential and efficiency of crude
resins from indigenous plants in the extraction of humic substances from soil. The points of zero charge
of crude resins from five plants (Anarcadiumoccidentale, Bowswellia sacra, magniferaindica, Euphorbia
tiricalli, and Haveabraziliensis) were determined using potentiometric method (batch titration method).
Batch experiments of resin (solid) – solution system was used to extract the humic substances. The results
revealed that with the exception of Bowswellia sacra, resins from the other plants have the potential to
extract humic acid and fulvic acid. Adsorption efficiency studies indicated that the plant resin with the
highest efficiency of extraction (83.88%) for humic acid is Euphorbia tiricalli. And for fulvic acid the
highest efficiency (77.29%) is Anarcadiumoccidentale. No net adsorption was noted for Bowswellia sacra
for HA and FA. Knowledge of the point of zero charge of the resins enhanced our understanding and
provided a potential alternative method of extracting commercial grade HA and FA from soil, to generate
income for poverty alleviation.
Key words:Humic substance, humic acid, fulvic acid, resin, adsorption, extraction.
1.0 INTRODUCTION
Humic substances (HSs) are the most widely-spread natural complexing ligands
occurring in nature. The remarkable properties of HSs have attracted the attention of
many scientists and industrialists (Apea, 2013). The results of research on humic
substances’ properties and applications over the years have brought new knowledge on
their physicochemical properties and pointed to the use of these interesting natural
compounds in many practical applications. And its commercialization is fast gaining
grounds.
Humic substances have been utilized in large-scale in the building, leather, woodwork,
ceramic, plastics, paper, and food processing industries. Some of the applications of
HSs in the environment include removal of heavy metal and radioactive elements from
water discharges from nuclear plants (Ghaddour and Davies 1999), sewage purification,
sorbing gases from animal-carcass rendering plant, hydrogen sulfide and mercaptans
from municipal gas supplies, and sulfur dioxide from stack gases (Green and Manahan
1981), and removal of organic pollutant (agrochemicals and pharmaceuticals). HSs also
play an important role in agriculture, and biomedically HSs are used on large-scale in
veterinary and human medicine (Mund-Hoym 1981, Brzozowskiet al., 1994) because of
theirantiviral, profibrinolytic, anti-inflamtory and estrogenic activities (Waksman 1998).
Theantibacterial (Ansorget al.,1978, Skliaret al., 1998) and antiviral (Klöcking and
Corresponding Author: Ohene B. Apea E-mail:[email protected]
Apea et al., (2012). Chemical extraction of humic substances using natural resins
Sprossig 1972, Thiel et al., 1977 1981, Schiller et al., 1979, Klicking 1991) properties
of humic substances represent new possibilities for their medical application.
Due to their poly-electrolytic properties, humic substances are one of the most powerful
chelating agents among natural organic substances (Tipping, 2002, Apea, 2013). The
zwitterionic character of humic substances allows the interaction of anions with
positively charged groups of humics and cations with negative charged groups of these
substances. The unique chemical properties of humic substance products enable their
application in industry, agriculture, environmental and biomedicine. Thus their
economic value for generating income cannot be over emphasized.
In this study attempt is made to show that this particular interesting material (HSs),
which like many others remain un-commercialized for economic growth, can be
harnessed using crude resins from indigenous plants.
2.0 ANALYTICAL METHODS
2.1 Sampling and preparations of resins
Resins were tapped from plants by slashing the bark. The exuded resins were allowed to
bleed out and collected. The resins were prepared for experiment by exposing to air to
harden. The surface area of the oxidized resins were reduced mechanically and
employed in the adsorption experiments. Resin samples were obtained from the
following plants cashew (Anarcadiumoccidentale), frankincense (Bowswellia sacra),
mango (magniferaindica), milk bush (Euphorbia tiricalli), and rubber
(Haveabraziliensis).
2.2 Experimental procedure for point of zero charge (PZC)
The PZC of the resins were determined using acid-base titration of the colloidal
dispersion while monitoring the pH of the suspension as indicated by Isaac (2011).
Several titrations (10 times) were carried out to obtain a satisfactory graph. The
experiment was repeated for all the resins and the PZC of the individual resins were
used to design the adsorption experiments
2.3 Extraction and Isolation of humic substances
Humic substance fractions were extracted and isolated from soil samples using a
procedure described by Apea (2013). The humic substance isolates were used in the
preparation of standard solutions of concentrations 120.66 mgC/l for fulvic acid, and
110.68 mgC/l for humic acid.
2.4 Determination of organic carbon
Quantitative analysis of the organic materials present in standard solutions, the
individual phases of solid-solution systems were determined by accounting for the total
organic material present in terms of organic carbon. The determination was carried out
using a modified Walkley-Black method by Forster (1995).
2.5 Experimental procedure for adsorption process
The adsorption process experiment was carried out by bringing 1.0g of the activated
resin (resin soaked in a solution of pH 1 for 10hrs) into contact with 10ml standard
solution of humic acid (3.162 mgC/ml) or fulvic acid (3.447 mgC/ml) for 10hrs. The
liquid phase of the resin-solution system was separated to terminate the experiment by
filtration using filter paper. The filtrate was then analyzed for its total organic matter
content in terms of organic carbon. The variations in the organic carbon value in the
solution phase before and after the experiment were used to discuss the extent of
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Apea et al., (2012). Chemical extraction of humic substances using natural resins
adsorption. The experiment was carried out in batches and repeated five times for each
resin-humic substance system.
3.0 RESULTS AND DISCUSSION
3.1 The point of zero charge (PZC) of plant resins
The outcome of the experiments indicated that the PZC of the crude plant resins occur
at low pH values (table 1). This implies that the crude resins have a high potential for
environmental remediation. In natural environments (terrestrial and aquatic) pH values
are normally higher than the pH of the observed PZCs. Under these conditions the
resins are expected to be negatively charged, thus their ability to form complexes with
the cations of metal pollutants will under normal environmental conditions be feasible.
However, below the PZC, the resins are expected to have high affinity for anions.
Table 1: PZC of plant resins
RESINS
PZC VALUES
CNPR
3.62
FR
4.16
MPR
3.22
MBPR
4.85
RBR
3.81
NB: MBPR = milk bush plant resin, RPR = rubber plant resin, FR = frankincense
resin, CNPR = cashew nut plant resin, and MPR = mango plant resin.
In this study, resins activated below the PZC of the crude resins were brought into
contact with aqueous humic substances to determine the relative effectiveness of the
different resins in humic matter removal from aqueous systems containing a resin.
3.2 Theoretical Considerations on the resin-humic substances aqueous system
The extraction systemis made up of aqueous phase and a solid phase. The aqueous
phase contained the organic ligand (FA or HA). The solid phase was a solid adsorbent
such as milk bush plant resin (MBPR), rubber plant resin (RPR), frankincense resin
(FR), cashew nut plant resin (CNPR) and mango plant resin (MPR).
When resins are introduced into the organic acid solution, adsorption of organic acid
ligands by the resins is expected to occur (figure 1). This is due to the positively
charged surface of the resins which attract the negatively charged ligands in the aqueous
phase (organic acid solution).
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Apea et al., (2012). Chemical extraction of humic substances using natural resins
Figure 1: Hypothetical reaction profile for the interaction between the solid resin
and aqueous humic substances.
The interaction of resins and organic ligands is conceived to be reversible and
eventually reaches equilibrium. Water soluble organic compounds (R*) in the impure
resinous material also go into the aqueous phase (figure 1). The release of soluble
organic species from the resins continue in a reaction considered in this study as being
irreversible and continues untilit reaches its maximum level when all R* are completely
in solution(figure 2). It was also assumed that, R* in the aqueous phase is not readsorbed by the resins. Thus, R* does not interfere in the adsorption at the resin’s
surface as well, and does not compete with the organic ligands for binding site on the
resins, another assumption made was that R* does not interact with the organic ligand
(L). R* increase the concentration of the total organic carbon in the aqueous phase.
Figure 2: Hypothetical reaction profile for the interaction between the solid resins
and aqueous humic substances.
It may therefore be stated that from the hypothetical reactions below, the concentration
of L
𝑅 + 𝐿(𝑎𝑞) = 𝑅𝐿(𝑠) , and 𝑅(𝑠) → 𝑅(𝑎𝑞)
in the aqueous phase reduces with time and becomes steady at equilibrium while R*
increases in the aqueous phase and reaches maximum concentration over time (figure
2). Thus accounting for the concentration of the species at equilibrium in order to
determine the extent of ligand adsorption require careful analysis when the species are
quantitatively determined in terms of total organic carbon. The relationships below are
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Apea et al., (2012). Chemical extraction of humic substances using natural resins
thus the conceived theoretical accounting of the quantitative study of the adsorption
process.
𝑀𝑇 = 𝑀𝐿𝐼 + 𝑀𝑓 … … … … … … … … 𝑖
𝑀𝐼 = 𝐿𝐼 … … … … … … … … … … 𝑖𝑖
𝑀𝑓 = 𝐿𝑎𝑞 + 𝑅 ∗ … … … … … … . 𝑖𝑖𝑖
𝑀𝑇 = 𝐿𝑎𝑞 + 𝐿𝑎 + 𝑅 ∗ … … . . 𝑖𝑣
𝐿𝑎 = 𝑀𝑇 − 𝐿𝑎𝑞 − 𝑅 ∗ … … … … … . . 𝑣
∴ 𝐿𝑎 = 𝑀𝑇 − 𝐿𝑎𝑞 … … … … … … . . 𝑣𝑖
𝐵𝑢𝑡, 𝑀𝑇 = 𝐿𝐼 + 𝑅 ∗ … … … … … … 𝑣𝑖𝑖
⇒ 𝐿𝑎 = (𝐿𝐼 + 𝑅 ∗ ) − 𝐿𝑎𝑞 − 𝑅 ∗ … … … … 𝑣𝑖𝑖𝑖
𝐿𝑎 = 𝐿𝐼 + 𝑅 ∗ − 𝐿𝑎𝑞 − 𝑅 ∗ … … . . 𝑖𝑥
𝐿𝑎 = 𝐿𝐼 − 𝐿𝑎𝑞 … … … … . 𝑥
(Where 𝑀𝑇 = 𝑡𝑜𝑡𝑎𝑙𝑚𝑎𝑠𝑠𝑜𝑓𝑜𝑟𝑔𝑎𝑛𝑖𝑐𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑𝑖𝑛𝑎𝑞𝑢𝑒𝑜𝑢𝑠𝑝ℎ𝑎𝑠𝑒, 𝑀𝐼 =
𝑡𝑜𝑡𝑎𝑙𝑚𝑎𝑠𝑠𝑜𝑓𝑜𝑟𝑔𝑎𝑛𝑖𝑐𝑙𝑖𝑔𝑎𝑛𝑑𝑖𝑛𝑎𝑞𝑢𝑒𝑜𝑢𝑠𝑝ℎ𝑎𝑠𝑒𝑏𝑒𝑓𝑜𝑟𝑒𝑎𝑑𝑠𝑜𝑟𝑝𝑡𝑖𝑜𝑛, 𝐿𝐼 =
𝑖𝑛𝑖𝑡𝑖𝑎𝑙𝑎𝑚𝑜𝑢𝑛𝑡𝑜𝑓𝑙𝑖𝑔𝑎𝑛𝑑𝑠, 𝑅 ∗ = 𝑑𝑖𝑠𝑠𝑜𝑙𝑣𝑒𝑑𝑜𝑟𝑔𝑎𝑛𝑖𝑐𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑, 𝐿𝑎𝑞= 𝑢𝑛 −
𝑎𝑑𝑠𝑜𝑟𝑏𝑒𝑑 𝑙𝑖𝑔𝑎𝑛𝑑 𝑖𝑛 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛, 𝐿𝑎 = 𝑜𝑟𝑔𝑎𝑛𝑖𝑐 𝑙𝑖𝑔𝑎𝑛𝑑 𝑎𝑑𝑠𝑜𝑟𝑏𝑒𝑑, 𝑀𝑓 =
𝑠𝑢𝑚 𝑜𝑓 𝑅 ∗ 𝑎𝑛𝑑𝐿𝑎𝑞 )
The total mass of organic compounds in the aqueous phase (MT) is the sum of the total
mass of organic ligand before adsorption and the total mass of organic compounds in
the system at the end of experiment any time adsorption has began (reaction i). The total
mass of organic ligand is the same as the initial amount of ligands present (reaction ii)
in the system before adsorption, whereas the total mass of the organic compounds any
time after adsorption had began (Mf) is the sum of the amount of un-adsorbed ligand
(Laq) and R* (reaction iii). Therefore, the total mass of organic compound in the system
is the sum of un-adsorbed ligand (Laq), amount of ligand adsorbed (La) and R* (reaction
iv). Hence, the mass of ligand adsorbed is the difference between total mass of the
organic compound, less the sum of un-adsorbed ligand and R* (reaction v). Therefore,
the amount of ligand adsorbed equals the difference between the total mass of organic
compound in the aqueous phase and the mass of un-adsorbed ligand. Meanwhile, the
total mass of organic compound is the sum of total ligands and R*. Therefore, the
amount of ligands adsorbed is the difference between the sum of the total amount of
ligand in the system (LT) and R*, and the sum of un-adsorbed ligand and R*. The
amount of ligand adsorbed becomes the difference between the total amount of ligand in
the system and the amount of un-adsorbed ligands.
3.3 Adsorption Efficiency of Resins
The results presented in table 2 shows that the extent to which HA is adsorbed by the
resins is in the order MBPR > CNPR > RPR. All the resins adsorbed HA. Their ability
to swell in aqueous solution significantly influences their extent of adsorption by
increasing the total adsorption sites. This ability subsequently increases the extent of
adsorption of HA by the resins. In addition, the variation in particle size of the resins
also affects their extents of adsorption. The smaller the particle size the greater the
surface area and therefore the higher the adsorption.
MBPR was noted to have the highest efficiency of adsorption (83.88%) and RPR had
the lowest efficiency (6.47%) in the adsorption of humic acid (table 3). The outcome
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Apea et al., (2012). Chemical extraction of humic substances using natural resins
indicates that MBPR is comparatively the most effective resin for adsorption of humic
acid.
Table 2: Mass (mgC/L) of adsorption of HA by plant resins
RESINS
MI (mgC/L)
CNPR
MBPR
RPR
FR
0.2047845
0.2047845
0.2047845
0.2047845
MR*
(mgC/L)
0.046907
0.1978416
0.038573
0.008963
Mf (mgC/L)
0.221628
0.230844
0.23011
0.2382177
Mads
(mgC/L)
0.0300635
0.1717821
0.0132475
-0.0244702
STANDARD
DEVIATION
0.65988
0.462989
0.50831
0.97452
Note:𝑀𝐼
= 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑜𝑟𝑔𝑎𝑛𝑖𝑐 𝑎𝑐𝑖𝑑 𝑠𝑡𝑎𝑛𝑑𝑎𝑟𝑑𝑠, 𝑀𝑅 ∗= 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑜𝑟𝑔𝑎𝑛𝑖𝑐 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 𝑑𝑖𝑠𝑠𝑜𝑙𝑣𝑒𝑑, 𝑀𝑓 =
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑜𝑟𝑔𝑎𝑛𝑖𝑐 𝑎𝑐𝑖𝑑 𝑓𝑖𝑙𝑡𝑟𝑎𝑡𝑒 𝑎𝑛𝑑 𝑀𝑎𝑑𝑠 = 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑜𝑟𝑔𝑎𝑛𝑖𝑐 𝑎𝑐𝑖𝑑 𝑎𝑑𝑠𝑜𝑟𝑏𝑒𝑑
There was an exceptional case noted in the adsorption of HA using FR. This gave a
negative absorption value of –0.0244702 mgC/g of HA. This implies there was no net
absorption and there are more organic species in the aqueous phase than there are in the
solid phase.
Table 3: Adsorption efficiency of HA by plant resins
RESINS
CNPR
MBPR
RPR
ADSORPTION EFFICIENCY ( % )
14.68
83.88
6.47
The extent of fulvic acid adsorption is also influenced by particle size of the resins.
However, it was noted that the resin with the highest adsorption efficiency for fulvic
acid is CNPR, 77.29%, MPR gave the least, 18.52%, (table 5). In general bothhumic
and fulvic acids can be absorbed by the resins, but to different extents. No net
adsorption was also noted for FR in the adsorption of fulvic acid.
Table 4: Mass of adsorption of FA acid by plant resins
RESINS
MI (mgC/L)
MR*
(mgC/L)
0.046903
0.010933
0.197842
0.038573
0.008963
Mf (mgC/L)
CNPR
0.316505
0.11880
MPR
0.316505
0.26882
MBPR
0.316505
0.387977
RPR
0.316505
0.279017
FR
0.316505
0.36688
Note:MI = 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑜𝑟𝑔𝑎𝑛𝑖𝑐 𝑎𝑐𝑖𝑑 𝑠𝑡𝑎𝑛𝑑𝑎𝑟𝑑𝑠, MR ∗=
Mads
(mgC/L)
0.244635
0.058618
0.132369
0.076061
-0.041412
STANDARD
DEVIATION
3.39179
0.84135
0.780593
0.72170
0.202082
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑑𝑖𝑠𝑠𝑜𝑙𝑣𝑒𝑑 𝑜𝑟𝑔𝑎𝑛𝑖𝑐 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 , Mf =
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑜𝑟𝑔𝑎𝑛𝑖𝑐 𝑎𝑐𝑖𝑑 𝑓𝑖𝑙𝑡𝑟𝑎𝑡𝑒 𝑎𝑛𝑑 𝑀𝑎𝑑𝑠 = 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑜𝑟𝑔𝑎𝑛𝑖𝑐 𝑎𝑐𝑖𝑑 𝑎𝑑𝑠𝑜𝑟𝑏𝑒𝑑
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Apea et al., (2012). Chemical extraction of humic substances using natural resins
Table 5: Adsorption efficiency of FA by plant resins
RESINS
CNPR
MPR
MBPR
RPR
ADSORPTION EFFICIENCY ( % )
77.29
18.52
41.82
24.03
3.4 Stability constant
The concentrations of the ligand in the system phases were used to estimate the stability
constants for the humic and fulvic acid systems (table 6). Based on the assumptions
made earlier in the theoretical considerations, the hypothetical reaction equation below
were used for the relationship employed to compute the stability constants.
𝑅𝑠 + 𝐿𝑎𝑞 ⇌ 𝑅𝐿𝑠
Where
𝑙𝑖𝑔𝑎𝑛𝑑𝑏𝑜𝑛𝑑
𝐾=
𝑅𝑠 = 𝑟𝑒𝑠𝑖𝑛𝑠𝑎𝑚𝑝𝑙𝑒, 𝐿𝑎𝑞 = 𝑙𝑖𝑔𝑎𝑛𝑑𝑜𝑓𝑜𝑟𝑔𝑎𝑛𝑖𝑐𝑎𝑐𝑖𝑑𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛, 𝑅𝐿𝑠 = 𝑟𝑒𝑠𝑖𝑛 −
𝑅𝐿𝑠
[𝑅𝑠 ][𝐿𝑎𝑞 ]
Where k = Stability constant
The greater the amount of ligand adsorbed in the aqueous system the higher the stability
constant (K) and vice versa. This confirmed that MPBR had the highest adsorption
efficiency for HA removal from solution and CNPR for FA removal (table 6). In this
case, the values of K imply that even though adsorption of a ligand may be appreciable
the resin ligand complex is unstable and generates more un-bound forms of the ligand.
Thus in such systems there will always be more reactants than products, and adsorption
will not lead HA and FA removal from solution. Consequently, a combination of CNPR
and MBPR may be used for the removal of humic substances from solution, or their
removal may be carried out selectively with CNPR for FA and MBPR for FA.
Table 6: Stability constant
RESINS
CNPR
MPR
MBPR
RPR
K
(FA)
1.30125
0.218
0.4309
0.2726
K
(HA)
0.8536
1.7342
0.2537
(Note: La = ligand adsorbed, 𝐿𝑎𝑞 = 𝑙𝑖𝑔𝑎𝑛𝑑𝑜𝑓𝑜𝑟𝑔𝑎𝑛𝑖𝑐𝑎𝑐𝑖𝑑𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 , K [Rs] = Stability
constant of resin)
3.5 Zero Net Adsorption
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Apea et al., (2012). Chemical extraction of humic substances using natural resins
The hypothetical equations suggest that the interaction between the resin (R) and
organic ligand (L) in the resin-aqueous solution system is also accompanied by the
release of water soluble organic impurities (R*) from the crude rein into the aqueous
phase. In addition, the resinous material may also undergo dissolution and introduce
more organic material (Raq) into the aqueous phase. The following hypothetical
equations are hence conceived for use in the interpretation of the possible cause of
negative adsorption.
𝑅𝑠 + 𝐿𝑎𝑞 ⇌ 𝑅𝐿𝑠 + 𝑅 ∗ ……………..1
Where
𝑅𝑠 = 𝑟𝑒𝑠𝑖𝑛𝑠𝑎𝑚𝑝𝑙𝑒, 𝐿𝑎𝑞 = 𝑢𝑛𝑎𝑑𝑠𝑜𝑟𝑏𝑒𝑑𝑙𝑖𝑔𝑎𝑛𝑑𝑖𝑛𝑎𝑞𝑢𝑒𝑜𝑢𝑠𝑝ℎ𝑎𝑠𝑒, 𝑅𝐿𝑠 = 𝑟𝑒𝑠𝑖𝑛 −
𝑙𝑖𝑔𝑎𝑛𝑑𝑐𝑜𝑚𝑝𝑙𝑒𝑥, 𝑅 ∗= 𝑤𝑎𝑡𝑒𝑟𝑠𝑜𝑙𝑢𝑏𝑙𝑒𝑜𝑟𝑔𝑎𝑛𝑖𝑐𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑(𝑖𝑚𝑝𝑢𝑟𝑖𝑡𝑖𝑒𝑠)𝑖𝑛𝑡ℎ𝑒𝑟𝑒𝑠𝑖𝑛
𝑅𝑆 + 𝐿𝑎𝑞 ⇌ 𝑅𝐿𝑠 +𝑅𝑎𝑞 + R*…………2
Where 𝑅𝑎𝑞 = dissolved resin
Careful considerations of the events suggest that the zero net adsorption observed is due
possibly to the following:





The resin-ligand complex formation induces or reinforces the water soluble
properties of the resin.
Ligand adsorption and desorption processes occur at equal rate giving the
impression of zero net adsorption.
There was no ligand adsorption at all, and partial dissolution of the resin as well
as the transfer of organic impurities (R*) into the aqueous phase is the major
changes affecting the total organic carbon content of the system.
The transfer of organic impurities (R*) into the aqueous phase increases in the
presence of humic substances.
The aqueous forms of the organic impurities and or the HSs have the tendency
to catalyze or induce the dissolution of the resin.
Therefore, it is possible that the frankincense which gave negative adsorption values
could have been as a result of any of the reasons above. Any mechanism or process
which increase the value of R* and Raq will result in the observation of negative
adsorption.
Then, the relation 𝐿𝑎 = (𝐿𝐼 + 𝑅 ∗ ) − 𝐿𝑎𝑞 − 𝑅 ∗
Will become𝐿𝑎 = (𝐿𝐼 + 𝑅 ∗ ) − 𝐿𝑎𝑞 − 𝑅 ∗ − 𝑅𝑎𝑞 , when there is no change R* = R*
∴ 𝐿𝑎 = 𝐿𝐼 − 𝐿𝑎𝑞 −𝑅𝑎𝑞
La = negative since LI< (Laq + Raq)
This presuppose that La = negative may imply adsorption in the presence of dissolving
solid phase.
Alternatively, when LI= 𝐿𝑎𝑞
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Apea et al., (2012). Chemical extraction of humic substances using natural resins
Then La=LT−𝐿𝑎𝑞 − 𝑅𝑎𝑞 = 0 – Raq = negative
The deductions indicate that ligand desorption can occur but they may be transferred
back into the aqueous phase as the resin goes back into solution, and this suggest that
the resin is not a good material for extraction in aqueous system at least under the
conditions of this experiment.
Resins such as frankincense can only be used when the chemistry of interaction between
the resin adsorption surface and the organic ligands as well as changes in the physical
and chemical properties of the resin upon interaction with ligands are understood. It is
therefore imperative for the study of such resin to be carried out to increase our
understanding of aqueous based adsorption.
4.0CONCLUSION
The successful determination of the point of zero charge of the crude resins indicated
that the crude resins have poly electrolytic characteristic which made it possible for the
adsorption of HA and FA. This adsorption was authenticated by the determination of
organic carbon of HA and FA in the resin solution before and after adsorption. HA was
best extracted by milk bush plant resin with adsorption efficiency of 83.88%. FA was
best extracted by cashew nut plant resin with adsorption efficiency of 77.29%.However,
there was no net absorption of HA and FA with frankincense. The extraction process
provides easy and cheap way of extracting HA and FA for commercial use with crude
resins.
5.0 ACKNOWLEDGMENT
The authors express their thanks to Head of Applied Chemistry Department, University
for Development Studies, for using their laboratory to carry out the experiments. We are
also indebted to the lecturers of the Department and all those who helped in the
sampling of the resins.
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