Chemical Speciation of Some metal ions in Groundwaters of Yola Area Using Geochemical Model

Chemical speciation of some metal ions in groundwaters of Yola area using geochemical model were carried out to determine the water quality of the area using the PHREEQC speciation model. The study findings based on model calculations indicated that free Na, Ca, Mg and K ions are present and the consequent bioavailability are 95.83% to 99.84% at the pH ranges of 6.1 to 7.8 of the tested wells. Iron as free Fe was bioavailable at 46.53% to 79.37% of the total iron. The lower values of free Fe ions are related to the organic complexation of the ions. The model findings suggest that Fe levels present a health risks in some water samples. The result also indicate that the concentration of Na, Ca, Mg and K at such level would be available for uptake by plants, animals and humans. @ JASEM Groundwater contains a wide variety of dissolved inorganic species in various concentrations, as a result of chemical and biochemical interactions between groundwater and the geological materials through which it flows, and to a lesser extent because of contributions from the atmosphere and surface water bodies (Freeze and Cherry, 1979). The presence of various inorganic constituents in groundwater is controlled by the reaction mechanisms such as dissolution/precipitation reactions and adsorption including the rates (kinetics) of the geochemical process (Appelo and Postma, 1993). Analytical techniques such as spectrometry and chromatography provide important information about the metals concentration in water, ions in groundwater can form unlimited number of species due to the hydrolysis, complexation and redox reactions (Baes and Mesmer., 1979). The selected five metals are of importance to water chemistry. Calcium is an essential alkaline-earth element for plant and animal life forms, and the solubility of its carbonate in water results in stalactites and stalagmites and hardness in water. Sodium is widely used in the manufacture of sodamide, sodium cyanide, sodium peroxide and sodium hydride as well as in the preparation of tetraethyl lead PbEt4 an important anti-knock agent in gasoline. Such applications tend to increase its level in the environment. Magnesium is produced from various activities especially in making organomagnesium compounds, useful in organic synthesis and is also an essential alkaline-earth element for plant and animal nutrition. Potassium is used in the manufacture of fertilizers usually as chlorides, sulphate, nitrate and carbonate and is extensively deposited in the environment. Iron is the cheapest and most abundant, useful (especially as an alloy in the production of steel) and important of all metals. Such qualities tend to increase its level in the environment. The PHREEQC speciation model was used to calculate ion activities. The PHREEQC model is a geochemical speciation model that is capable of computing specific equilibrium ion activities among the dissolved and adsorbed species and their equilibrium solid phase. The model is able to consider the interaction of major cations with anions (Cl , SO4 2, HCO3 and CO3 2) as a function of temperature, ionic strength and pH. The aim of this study is to estimate the activities of various ionic species of sodium, calcium, magnesium, potassium and iron in groundwater using geochemical models from the measured ion concentrations. The Study Area: The study area fall within longitudes 12 o 20’E and 12 o 34’E and latitudes 9 o 11’N and 9 o 24’N and lies about 50 km south of the Hawal Massifs. It is bounded to the east by the Republic of Cameroun and to the west by Ngurore town. The northern boundary is demarcated by Gokra town and the southern boundary by the Mandarare town and occupies approximately 431 km 2 of the land surface. MATERIALS AND METHODS The investigation of groundwater chemistry in the study area started with the chemical analyses of ninety-six water samples collected from shallow hand-dug wells (80), deep wells (11), surface waters (11) and precipitation (5) in Yola Area; Figure 1. Samples collection was aimed at covering and representing the lateral and vertical extent of the hydrostratigraphic units within the study area along with surface water and rainfall. The samples from the deep wells in which pumps are already installed, were collected after a few hours of pumping and the screen interval of the well represents the average sample depth. Samples from the shallow hand-dug wells were bailed, using a stainless steel bailer, from a depth of a few meters below the water table, which more or less indicates the sample depth (Abdalla, 2009). The samples were collected in 1000ml plastic bottles and field filtration was carried out through filter papers (0.45um) to remove suspended solids. They were then carefully sealed, labeled and taken for analyses. Chemical analyses were performed in the laboratory of the Adamawa State Water Board Yola, Nigeria employing standard methods, Atomic Absorption Spectrophotometry for cations (Na + ,Ca 2+ ,Mg 2+ ,K + ,Fe) and conventional Chemical Speciation of Some metal ions..... 1 GABRIEL IKE OBIEFUNA; 2 DONATUS MADUKA ORAZULIKE titration for anions (HCO3 ,SO4 2,Cl ,NO3 ). Ions were converted from milligram per litre to milliequivalent per litre and anions balanced against cations as a control check of the reliability of the analyses results. Geochemical Modeling: The hydrogeochemical computer model PHREEQC (Parkhurst and Appelo 1999) performs speciation calculations based on the law of mass action which states that for a reaction of the generalized type: aA + bB ↔ cC + dD (1) the distribution at equilibrium of the species at the left and right side of the reaction is given by: K = [C] c [D] d /[A] a [B] b (2) where; K = equilibrium constant and the bracketed quantities denote activities or effective concentrations. In the present investigations we equate activities with molal concentrations. PHREEQC (Parkhurst and Appelo 1999) is a computer model for performing hydrogeochemical calculations such as exchange and surface complexations, mineral reactions and equilibrations and mixing of water. PHREEQC operates with input files in which the calculation instructions are arranged according to key-words. These keywords are largely self-instructive as is illustrated by the example input file below where the keywords have been capitalized. Several databases are available with constants for the various reactions. The aqueous concentrations in a solution are defined with SOLUTION. The symbols for the elements are listed in the first column of SOLUTION_MASTER_SPECIES in the database. SOLUTION 1 Speciate and analyses, calculate saturation indices Temp 25 ♯ temperature in degrees celcius, default = 25 o C pH 7.0 ♯ default pH = 7 pe 4.0 ♯ pe = -log (electron activity) , default = 4 -units mmol/kgw ♯ default units mmol/kg water Ca 3.0 ♯ total dissolved Ca Na 1.0 K 2.0 Mg 4.0 Alkalinity 3.8 as HCO3 ♯ mmol charge / kgw S 1.0 ♯ total sulphur, mainly sulphate, S (6), at pe = 4 N (5) ♯ nitrogen in the form of nitrate, N (5) Cl 1.0 Water 1 ♯ kg water default = 1 kg Density 1 ♯ density, default = 1 kg/L END PHREEQC has been enhanced with several new features to increase applicability, such as onedimensional transport with dispersion and diffusive exchange with stagnant zones, exchangers and surfaces that can be coupled to varying amounts of minerals or reactants, and generalized kinetics (Parkhurst and Appelo 1999). This version has been used to calculate the data shown in Tables 2, 3 and 4. RESULTS AND DISCUSSION Analytical data are provided in Table 1. The pH values for tested samples varied from 6.1 to 7.8 for shallow groundwater, 6.8 to 7.8 for deep groundwater and 7.20 to 8.00 in surface water samples. Sodium concentrations range was between 0 and 157 mg/l in shallow groundwater 0.001 91.00 mg/l in deep groundwater and 2.23 to 211 mg/l for the surface waters respectively. In shallow groundwater potassium concentration ranges from 0 to 37 mg/l, 0 to 12.10 mg/l in deep groundwater and 1.20 to 9.00 mg/l for the surface waters respectively. The concentration of calcium in shallow groundwater samples are less than 25 mg/l, less than 39 mg/l in deep groundwater samples and between 1.20 to 9 mg/l in the surface water samples respectively. Magnesium concentration in shallow groundwater is less than 51mg/l, less than 55 mg/l in deep groundwater and between 12 and 84 mg/l in the surface water samples respectively. Iron concentrations range was between 0.001 and 1.80 mg/l in shallow groundwater, 0 and 0.32 mg/l in deep groundwater and 0 to 0.73 in the surface water samples respectively. Table 1: Physicochemical parameters of Surfacewater and groundwater Samples (values in mg/l unless otherwise stated) Parameter Shallow Groundwater Deep Groundwater Surfacewater Temp ( o C) (30-31) 30 ± 0.06 (30-32) 30.20 ± 0.60 (26-34) 29.56 ± 3.02 pH (6.10-7.08) 7.09 ± 0.39 (6.60-7.80) 7.22 ± 0.41 (7.20-8.00) 7.57 ± 0.23 EC (ds/m) (0.05-0.21) 0.09 ± 0.03 (0.04-0.18) 0.09 ± 0.04 (0.07 – 0.45) 0.22 ± 0.11 TDS (33-137)60±18.83 (27-121) 63 ±26 (41 298) 155 ± 72.60 Na + (0-157)34 ± 33.74 (0-91) 34 ± 34.30 (2.23 – 211) 73 ± 89.04 K + (0-37)4 ± 6.89 (0-12) 4.32 ± 4.16 (1.20 – 9.00) 5 ± 2.40 Mg 2+ (0.50-51)21 ± 9.00 (8-55) 31 ± 13.46 (12 -84) 35 ± 19. 09 Ca 2+ (0.48-25) 12 ± 6.19 (0.50-38)11.30 ± 11.70 (8 – 37) 26 ± 9.25 Fe (0-1.80) 0.35 ± 0.41 (0-0.32)0.09 ± 0.10 (0.0.73) 0.30 ± 0.26 Fe 2+ (0-0.70) 0.12 ± 0.16 (0-0.11)0.03 ± 0.04 (0 – 0.40) 0.17 ± 0.15 Fe 3+ (0-1.14) 0.22 ± 0.27 (0.21)0.06 ± 0.05 (0 – 0.44) 0.14 ± 0.13 NO3 (0-23) 4.36 ± 4.63 (0.66-31) 6 ±8.63 (9 – 59) 35 ± 17.97 Cl (0-239) 68 ± 56 (0-172)76 ± 61.82 (28 – 455)146 ± 138.28 HCO3 (19.90-251) 93.4 ± 41 (50-207)103 ± 44.4 (49 – 273) 137 ± 63.27 SO4 2(0-61) 11 ± 12.28 (0-65)14.80 ± 19.66 (2 29) 18 ± 7.52 66 Chemical Speciation of Some metal ions..... 1 GABRIEL IKE OBIEFUNA; 2 DONATUS MADUKA ORAZULIKE Table 2: Result of PHREEQC output file containing activities and concentrations of some ionic species in Sha

Groundwater contains a wide variety of dissolved inorganic species in various concentrations, as a result of chemical and biochemical interactions between groundwater and the geological materials through which it flows, and to a lesser extent because of contributions from the atmosphere and surface water bodies (Freeze and Cherry, 1979).The presence of various inorganic constituents in groundwater is controlled by the reaction mechanisms such as dissolution/precipitation reactions and adsorption including the rates (kinetics) of the geochemical process (Appelo and Postma, 1993).Analytical techniques such as spectrometry and chromatography provide important information about the metals concentration in water, ions in groundwater can form unlimited number of species due to the hydrolysis, complexation and redox reactions (Baes and Mesmer., 1979).The selected five metals are of importance to water chemistry.Calcium is an essential alkaline-earth element for plant and animal life forms, and the solubility of its carbonate in water results in stalactites and stalagmites and hardness in water.Sodium is widely used in the manufacture of sodamide, sodium cyanide, sodium peroxide and sodium hydride as well as in the preparation of tetraethyl lead PbEt 4 an important anti-knock agent in gasoline.Such applications tend to increase its level in the environment.Magnesium is produced from various activities especially in making organomagnesium compounds, useful in organic synthesis and is also an essential alkaline-earth element for plant and animal nutrition.Potassium is used in the manufacture of fertilizers usually as chlorides, sulphate, nitrate and carbonate and is extensively deposited in the environment.Iron is the cheapest and most abundant, useful (especially as an alloy in the production of steel) and important of all metals.Such qualities tend to increase its level in the environment.The PHREEQC speciation model was used to calculate ion activities.The PHREEQC model is a geochemical speciation model that is capable of computing specific equilibrium ion activities among the dissolved and adsorbed species and their equilibrium solid phase.The model is able to consider the interaction of major cations with anions (Cl -, SO 4 2-, HCO 3 -and CO 3 2-) as a function of temperature, ionic strength and pH.The aim of this study is to estimate the activities of various ionic species of sodium, calcium, magnesium, potassium and iron in groundwater using geochemical models from the measured ion concentrations.

MATERIALS AND METHODS
The investigation of groundwater chemistry in the study area started with the chemical analyses of ninety-six water samples collected from shallow hand-dug wells (80), deep wells (11), surface waters (11) and precipitation (5) in Yola Area; Figure 1.Samples collection was aimed at covering and representing the lateral and vertical extent of the hydrostratigraphic units within the study area along with surface water and rainfall.The samples from the deep wells in which pumps are already installed, were collected after a few hours of pumping and the screen interval of the well represents the average sample depth.Samples from the shallow hand-dug wells were bailed, using a stainless steel bailer, from a depth of a few meters below the water table, which more or less indicates the sample depth (Abdalla, 2009).The samples were collected in 1000ml plastic bottles and field filtration was carried out through filter papers (0.45um) to remove suspended solids.They were then carefully sealed, labeled and taken for analyses.Chemical analyses were performed in the laboratory of the Adamawa State Water Board Yola, Nigeria employing standard methods, Atomic Absorption Spectrophotometry for cations (Na + ,Ca 2+ ,Mg 2+ ,K + ,Fe) and conventional titration for anions (HCO 3 -,SO 4 2-,Cl -,NO 3 -).Ions were converted from milligram per litre to milliequivalent per litre and anions balanced against cations as a control check of the reliability of the analyses results.

Geochemical Modeling:
The hydrogeochemical computer model PHREEQC (Parkhurst and Appelo 1999) performs speciation calculations based on the law of mass action which states that for a reaction of the generalized type: aA + bB ↔ cC + dD (1) the distribution at equilibrium of the species at the left and right side of the reaction is given by: K (2) where; K = equilibrium constant and the bracketed quantities denote activities or effective concentrations.In the present investigations we equate activities with molal concentrations.PHREEQC (Parkhurst and Appelo 1999) is a computer model for performing hydrogeochemical calculations such as exchange and surface complexations, mineral reactions and equilibrations and mixing of water.PHREEQC operates with input files in which the calculation instructions are arranged according to key-words.These keywords are largely self-instructive as is illustrated by the example input file below where the keywords have been capitalized.Several databases are available with constants for the various reactions.♯ kg water default = 1 kg Density 1 ♯ density, default = 1 kg/L END PHREEQC has been enhanced with several new features to increase applicability, such as onedimensional transport with dispersion and diffusive exchange with stagnant zones, exchangers and surfaces that can be coupled to varying amounts of minerals or reactants, and generalized kinetics (Parkhurst and Appelo 1999).This version has been used to calculate the data shown in Tables 2, 3 and 4.

RESULTS AND DISCUSSION
Analytical data are provided in Table 1.The pH values for tested samples varied from 6.1 to 7.8 for shallow groundwater, 6.8 to 7.8 for deep groundwater and 7.20 to 8.00 in surface water samples.Sodium concentrations range was between 0 and 157 mg/l in shallow groundwater 0.001 91.00 mg/l in deep groundwater and 2.23 to 211 mg/l for the surface waters respectively.
In shallow groundwater potassium concentration ranges from 0 to 37 mg/l, 0 to 12.10 mg/l in deep groundwater and 1.20 to 9.00 mg/l for the surface waters respectively.The concentration of calcium in shallow groundwater samples are less than 25 mg/l, less than 39 mg/l in deep groundwater samples and between 1.20 to 9 mg/l in the surface water samples respectively.Magnesium concentration in shallow groundwater is less than 51mg/l, less than 55 mg/l in deep groundwater and between 12 and 84 mg/l in the surface water samples respectively.Iron concentrations range was between 0.001 and 1.80 mg/l in shallow groundwater, 0 and 0.32 mg/l in deep groundwater and 0 to 0.73 in the surface water samples respectively.5.It indicate that 99.94% of potassium exists as free (K + ), about 0.05% as sulphate, 0.003% as KHPO 4 and about 0.0005% as KOH.In deep groundwater the chemical speciation of potassium with different anions indicate that 99.93% of potassium exists as free ions (K + ), 0.07% as sulphate, 0.003% as KHPO 4 and 0% as KOH respectively.In surface water samples an estimated 99.93% of potassium occurs in free ionic form (K + ), 0.06% occurs as KSO 4 , 0.02% as KHPO 4 and 0% as KOH respectively.).Ferrous ions (Fe 2+ ) form complexes with a number of ligands, a strong FeHCO 3 and FeCO 3 appears likely to be the major form in natural water containing dissolved CO 2 .Chemical speciation of iron in shallow groundwater samples indicated that 79.37% of iron is in the free ionic form (Fe +2 ), 12.18% as bicarbonate and less than 8% as phosphates, carbonates, sulphides and sulphates respectively.In deep groundwater 46.53% exists as free Fe 2+ ions, 41.31% as sulphides, 7.39% as bicarbonates and less than 4% as phosphates, carbonates and sulphates.In surface water samples an estimated 22.58% of iron occurs in free ionic form (Fe 2+ ), a predominant 67% occur as sulphides while the remaining 10.42% occur as phosphates, bicarbonates and carbonates respectively.Iron is an extremely mobile ion and its removal from groundwater is in most cases an extremely difficult tasks.Under mild oxidizing conditions iron is in a +3 valence state and forms an insoluble precipitates, Fe 2 O 3 while under reducing conditions is converted to +2 valence states and is present as soluble Fe 2+ cation.Increased iron concentrations in water samples are due to re-dissolution of previously formed unstable precipitates or due to leaching of iron from the adjacent rocks that bounds the aquifers of the study area.
Area: The study area fall within longitudes 12 o 20'E and 12 o 34'E and latitudes 9 o 11'N and 9 o 24'N and lies about 50 km south of the Hawal Massifs.It is bounded to the east by the Republic of Cameroun and to the west by Ngurore town.The northern boundary is demarcated by Gokra town and the southern boundary by the Mandarare town and occupies approximately 431 km 2 of the land surface.
The aqueous concentrations in a solution are defined with SOLUTION.The symbols for the elements are listed in the first column of SOLUTION_MASTER_SPECIES in the database.SOLUTION 1 Speciate and analyses, calculate saturation indices Temp 25 ♯ temperature in degrees celcius, default = 25 o C pH 7.0 ♯ default pH = 7 pe 4.0 ♯ pe = -log (electron activity) , default = HCO 3 ♯ mmol charge / kgw S 1.0 ♯ total sulphur, mainly sulphate, S (6), at pe = 4 N (5) ♯ nitrogen in the form of nitrate, N (5) Cl 1.0 Water 1

Table 1 :
Physicochemical parameters of Surfacewater and groundwater Samples (values in mg/l unless otherwise stated)

Table 2 :
Result of PHREEQC output file containing activities and concentrations of some ionic species in Shallow Groundwater samples(After Obiefuna in Preparation)

Table 3
Summary of PHREEQC output file containing activities and concentrations of some ionic species in Deep Groundwater Samples (After Obiefuna in Preparation)

Table 4 :
Summary of PHREEQC output file containing activities and concentrations of some ionic species in surface water (After Obiefuna in Preparation)