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Tanz. J. Sci. 38(3), 2012

SALT OF THE AFRICAN SYSTEM: A VALUABLE RESEARCH OPPORTUNITY FOR INSIGHT INTO ’S CONCENRTATED MULTI-ELECTROLYTE SCIENCE

JYN Philip and DMS Mosha Chemistry Department, University of Dar es Salaam, P.O. Box 35061 Dar es Salaam,

ABSTRACT The Tanzanian rift system lakes present significant cultural, ecological, recreational and economical values. Beyond the wealth of minerals, resources of these rift salt lakes include unique wildlife, for instance Lesser ( Phoenicopterus minor ) and ( spp ), which adapted chemically aggressive environments like that of . The general hydrochemical + + 2+ 2+ 2- - - equilibria of these salt lakes is governed by Na > K >> Ca ~ Mg : (CO 3 + HCO 3 ) > Cl > 2- - SO 4 ~ F ionic concentration pattern. Salt accumulation mechanism in these endorheic lakes is considered to base on thermo-mechanical disintegrative stress of the geochemistry sourcing. The rains chemically interact with rift terrains, which are dominated with natrocarbonatitic volcanic materials, thus transporting dissolved salts to the lakes. In addition, hot springs around the shores of these lakes carry significant loads into the lakes. The salt reserves magnifies through recurring evaporative concentration in seasonal cycles. Despite this huge wealth of mineral resource potential of the Tanzanian rift salt lakes, they are still underutilized, thus contributing less into the national economy. It is envisaged that studies on phase rule on separation of pure salts from lake as demonstrated herein have a direct industrial value addition to Tanzanian rift salt lakes.

INTRODUCTION electrolyte resource into the Tanzanian Economically significant reserves of the economy. This is indeed in conflict with the multi-electrolyte concentrates/ pressing country-wide demand for soda ash that typify the lakes of the African rift and allied minerals as key industrial system are to be found in Tanzania in host feedstock, which currently wholly relies on locations fitting the description importation. This realization has prompted a “endorheic” (closed) basins. Most prominent re-launch of local investigative chemical among these are lakes Natron, Manyara and scientific effort by local research groups to Eyasi plus smaller ones of lesser expanse provide quantity and quality evaluation and and prominence such as Kitangiri, updating, as well as harness the scholarship Balangida, Singidani, Balangidalelu, Basotu value availed by the challenging domain of and Basoda. natural hyper-saline multi-electrolyte science. Whereas the chemistry and aquatic science of salt lakes globally elsewhere have Important scientific contrast and departures benefited from substantial scientific from dilute aqueous text book chemistry research; critical knowledge gaps, scanty have been shown to characterize and apply and outdated scientific literature and to hyper-concentrated multi-electrolyte diminished prioritization for the Tanzanian chemical environments. The chemistry of resources have been responsible for the extremely concentrated electrolytes is stagnation in research . As a known to approach that of salt melts, a result there is meager input of this frontier scientific domain that demands the

1 Philip and Mosha - Salt Lakes of the African Rift System …

development of newer models for a clear of the Tanzanian and regional salt understanding of the governing equilibria. lakes fall under the category of “ soda lakes ” Chemical , the new equilibria and of high pH ≥ 10 (from anionic dominance of processes such as pH, p Ka ’s buffer ). The Na + > K + >> Ca 2+ ~ Mg 2+ : 2- - - 2- - capacities, the extreme aggressive chemical (CO 3 + HCO 3 ) > Cl > SO 4 ~ F ionic environment and adaptive mechanisms concentration pattern is typical (Table 1) evolved by resident bioforms, the phase rule save for few cases such as Lake Singidani 2- - tool for extraction and separation science for where [CO3 + HCO 3 ] is minor and closely pure salts may be cited among interesting mirrors the non-soda Dead rewarding key research themes thus chemistry. catalyzed and pursued in the project. Many

Table 1 : Trend of brine ionic concentrations in Tanzanian (Kameka 2006).

Cations Anions 2+ + 2+ + - - 2- 2- Mg > Na > Ca > K Cl > Br >> SO 4 ~ CO 3 + + 2+ 2+ 2- - - 2- - L. Natron Na > K >> Ca ~ Mg (CO 3 + HCO 3 ) > Cl > SO 4 ~ F + + 2+ 2+ 2- - - - 3- Ethiopian Lakes Na > K > Ca ~ Mg (CO 3 + HCO 3 ) > Cl > F > PO 4 + + 2+ - 2- 2- - Australian Lakes Na > K > Ca Cl > SO 4 > (CO 3 + HCO 3 ) + + 2+ 2+ - 2- - 2- - L. Eyasi Na > K >> Ca ~ Mg Cl > (CO 3 + HCO 3 ) > SO 4 >F + 2+ 2+ + - 2- 2- - - L. Singidani Na > Ca ~ Mg > K Cl > SO 4 > (CO 3 + HCO 3 ) > F + + 2+ 2+ - 2- - 2- 3- L. Balangida Na > K >> Ca ~ Mg Cl > (CO 3 + HCO 3 ) > SO 4 > PO 4 + 2+ + 2+ - 2- - 2- - 3- L. Kitangiri Na > Ca > K > Mg Cl > (CO 3 + HCO 3 ) > SO 4 > F > PO 4 + + 2+ 2+ 2- - - 2- 3- - L. Manyara Na > K > Ca ~ Mg (CO 3 + HCO 3 ) > Cl > SO 4 > PO 4 > F + + 2+ 2+ 2- - - 2- - L. Magadi Na > K >>Ca ~ Mg (CO 3 + HCO 3 ) > Cl > SO 4 > F + 2+ 2+ + - 2- 2- - - - Sea Na >> Mg > Ca ~ K Cl >> SO 4 > (CO 3 + HCO 3 ) > Br > F

Ionic concentrations are location and season individual salt lakes. These lakes are proving dependent, peaking downstream in open to host competitively ample resources stabilized lake brines and swinging with the locally, regionally and globally, and in some dry and wet seasons where they become of the instances such as , the concentrated during dry spells and vice tonnages excel any single source elsewhere versa during the wet season. The salt worldwide in terms of soda ash reserve accumulation mechanism hinges in salt lake volumes. basin dischargelessness of the which guarantees solute retention, RESOURCES OF THE RIFT SALT while the negative hydrological balance, LAKES high desiccating temperatures and aridity of lakes (Fig. 1) and rift localities is responsible for hyped levels Tanzanian lakes in particular, support a of the evaporative processes to yield the flourishing tourism industry centred on a electrolyte concentrates. Selective salt unique wildlife endowment particularly the precipitation into bedded sediments is cross border migratory another modifier of the chemical (Phoenicopterus minor ) populations and a constitution patterns. The mineral salt rich bird life associated with lake resource potential of local salt lakes as . Apart from the resident sought out by our local effort as well as varieties, for example Cichlids such as literature sources is presented here in terms Alcolapia spp of lake Natron, that can adapt of tonnage estimates for the major to these extreme chemically aggressive economically significant salts for the

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Tanz. J. Sci. 38(3), 2012

environments, fishing is not an economically significant industry on the soda lakes.

Figure 1 : Closed lake basins of the East African Rift System.

The mineral potential of Tanzanian salt and the largest known such lakes remain largely unexploited to-date deposit in the Southern Development except the Minjingu phosphate deposits (Orr Cooperation (SADC) . and Grantham 1931, Qulwi 1995) which is an ancient dried-up lake bed extension of

3 Philip and Mosha - Salt Lakes of the African Rift System …

Unlike () where mining of nature’s cheaper supplies. In the commercial exploitation commenced in African region, Lake Magadi continues to 1914, commercial salt production has dominate the production while Sua Pan remained virtually insignificant for the (Botswana) and Abiata () are abundantly rich Tanzanian salt and soda significant producers. An estimate of the lakes, save for peripheral domestic breakdown of the reserves in Tanzanian salt utilization such as medicinal, snuff additive, lakes (Kameka 2006, Mwakoba et al. 1992), laundry soda and food cookability improver. in terms of tonnage, is presented in Table 2. Soda ash is the principal industrial feedstock Lake Natron is singularly impressive and chemical now wholly globally sourced from surpasses most others in the rift zone and in nature’s reserves as the cheaper the region beyond (globally), and the alternative, after the more expensive Solvay economic development of its key industrial and Le Blanc Na 2CO 3 industrial production mineral reserves promises a new era of process options were abandoned after meaningful resource prosperity. proving unattractive cost-wise compared to

Table 2: The mineral potential of Tanzanian rift lakes in tonnage estimates (Kameka 2006).

L. Natron L. Balangida L. Eyasi NaCl 20,000,00 240,000 2,471,000 2- - Na - (CO 3 + HCO 3 ) 26,000,000 208,000 2,118,000 Na 2SO 4 900,000 152,000 n.d. KCl n.d. 8700 n.d. Na 3PO 4 30,000 n.d. n.d. n.d = not determined

Hydrochemical equilibria Mosha et al . 1996) and defy conventional − − For soda lakes, carbonates ( CO 2 + HCO ) dilute chemical methods of interpretation. 3 3 are the dominant brine electrolytes FACTORS AFFECTING THE concentration-wise in the majority of cases. COMPOSITION OF LAKE BRINES The governing brine chemical equilibria, pH such as pH, , fluoride, phosphate This is strictly a measure of a where a = and silicate, modified by high brine ionic H+ activity. It is known that a ≠ effective [H +] strength conditions, has been explored H+ if the activity coefficient ƒ ≠ unity, due to (Guest and Stevens 1951, Kameka 2006, restrictions on ion mobility and reactivity. In Mosha et al . 1996, Mwakoba et al . 1992, our work, we have adopted that a two pH Ngambeki 1996, Qulwi 1995). unit downward adjustment is required

(Mwakoba et al ., 1992) for a direct The equilibria are fundamentally important conventional pH meter readout (which bases and have a governing determining role on on the manufacturer’s calibrants) to cater for solubility, formation, sedimentation, ion- this fundamental complication. Extent of solvent behaviour, toxicity of various forms, reaction in these hyper saline multi-ion ecological mobilization and bio-availability media is known to increase with pathways which are critical for food webs in concentration of non-participating the basin . In highly concentrated (indifferent) electrolyte, which maximizes multi-electrolytes, these processes are charge separation. It is known that pH subject to major alteration (Horne 1969, measurement is sensitive to both [H +] and inter-ionic forces. Changes occur in the 4

Tanz. J. Sci. 38(3), 2012

liquid junction potential at the salt bridge - 2. It is among the most important equilibria test solution interface. An asymmetric in the soda lakes. An excellent treatment of potential arises in the glass electrode during the carbonate equilibrium and its transfers (from dilute to concentrated consequences in soda lakes is given solutions). elsewhere (Eugester, 1970). The results of our work point generally to discernible Carbonate equilibria suppression of the carbonate dissociation − − Carbonate ( CO 2 + HCO ) dominates as the constants (p Ka 1 and Pka 2) with ionic 3 3 strength as shown in Table 3. governing equilibrium in soda lakes on the abundance criterion as shown in Table 1 and

Table 3 : Carbonate p Ka data for selected rift soda lakes.

c TDS g/L pKa 1 pKa 2 L. Balangida (30 °C) 10.29 443.4 5.26 (5.18) 8.36 (8.41) 5.09 230.4 5.38 (5.43) 8.83 (8.77) L. Manyara (30 °C) 1.389 55.7 6.09 (6.14) 9.23 (9.30) 1.024 43.1 6.00 (6.06) 9.49 (9.38) Thermodynamic (25 °C) 0 0 6.37 10.25

Phosphate equilibria and buffer tolerance of aquatic bio-forms, mitigating capacities against large sudden potentially fatal Apart from its importance in the lake basin disruptive pH swings. These chemistry food webs, phosphate and the three-step tolerance mechanisms complement the bio- phosphate dissociative equilibrium is an adaptations that have evolved in response to important determinant of the buffer capacity, the extreme aggressive environments, so vital for survival of bio-forms in the permitting species, albeit few, to survive chemically aggressive and challenging brine therein. environment. Limitations of our procedure (potentiometry) permits only evaluation of Silicate equilibria pKa 1 and p Ka 2 while p Ka 3 eludes the Silicate equilibria have an important role in method due to indiscernibility, based on the salt lake ecosystem. It mobilizes silicon inadequacy of separation of equivalence for bio-uptake as the basis for the various points (> six log units minimum separation food webs in the aquatic environment, requirement for adjacent equivalent points to starting at the lowest trophic level(s). The be discernible). In common with findings by element is also bio-mobilized for other workers (Bates 1948) who examined incorporation into skeletal structures. For sea water, the acid dissociation constants of reasons aforementioned regarding phosphoric acid increase with ionic strength indiscernability of some of the equivalent − (salinity). A higher p Ka denotes a weaker points for the PO 3 case, the method acid. Buffer capacity based on the phosphate 4 enabled evaluation of p Ka and p Ka using equilibrium was shown to increase with 1 2 silicic acid in artificially re-constituted ionic strength and attains impressive “brines” of varying ionic strength to magnitudes ranging from 36 to 1000 times reproduce the target natural brines. The that of pure water which has the magnitude values obtained were in agreement to those of 4.6 x 10 -7. These magnitudes maximize of other investigators (Bates 1948) and to

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the thermodynamic value (after effecting terrain, with the dilute rain leacheate inflow appropriate extrapolations). accumulating in the endorheic basin, eventually summing up to present day Salt accumulation mechanisms reserves via repetitive evaporative Climate-driven and geochemistry sourcing concentration seasonal cycles over categories have been advanced to account millennia. Hot, windy desiccating for the current levels of accumulated conditions, and negative hydrological electrolytes. In the former version, rain balance (evaporation exceeding chemically interacts with rocks, pre- precipitation) and aridity, are fingerprint subjected to thermo-mechanical features of rift basin locations. Salt lake disintegrative stress by day versus night brines are richer in Na + than K + despite temperature differences, typically over 50 almost equal natural crustal abundance °C versus below 10 °C, respectively. Such (quoted at 2.9 and 2.6% respectively), as the rock weathering is typically depicted and latter bonds more efficiently and is more exemplified in rock formations in rift terrain strongly retained by silicate rocks, thus such as the weathered, disintegrated rock selectively resisting leach processes into face seen in Fig. 2 in the Lake Natron aquatic bodies. precinct. The short rains work and leach the

Figure 2 : Progress and effects of weathering of Lake Natron Basin rock formations; a hill in the lake basin (left) and close up details of the vertical rock face revealing the extent of the disintegrative thermo-mechanical stress influence (right).

The geochemistry of the locations of these singularity is highlighted by the world’s best salt lakes has a defining influence on the known example of a natrocarbonatite lava constitution of the accumulated salts. With type volcano that spews out this mineral the natrocarbonatitic volcanicity that type during eruptions; the Oldoinyo Lengai dominates the Tanzanian rift system, the (Fig. 3) in the Lake Natron basin, this being same will be reflected in salt lake electrolyte among the only two known world-wide, the constitution in which soda ash type minerals other being Homa Mountain in the Winam will expectedly command dominance. The Gulf.

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Figure 3 : Natrocarbonititic volcanicity: Lake Natron’s Oldoinyo Lengai Volcano (seen with the 2007 eruptive lava flows) which contributes into the lake basin’s soda ash dominance as is manifest in the vast soda ash evaporites reserves in the lake (Fig. 4).

(a)

(b)

Figure 4: The vast soda ash reserve expanses of Lake Natron. (a) Saturated brine in equilibrium with the crystallizing soda, (b) Dry soda ash on the surface.

The geochemistry of a salt lake location may chemistry and regeneration in the lake basin. exert its influence on the lake’s electrolyte Rain with its carbonic acid (H 2CO 3) load accumulation mechanism via the geothermal derived from dissolved is a springs which feed into the lake brine and key player and source in the basin mineral whose total contribution can sum up to a regeneration/replenishment mechanisms. dominating bulk for the target salt lake. The acid contents of the atmospheric Some of the well quoted striking examples precipitation (brief rains) flow lake ward are the respective contributions supported by through rock terrain, leaching and daily salt load inputs of 1000 and 500 tons chemically interacting with rock mineral into Lakes Natron and Magadi respectively content en-route that has been pre-released via the thermal spring sources that dot the by the disintegrative thermo-mechanical periphery of the lake. stress mechanisms described earlier. All the enumerated mechanisms operating in a lake Atmospheric carbonic acid sourcing is basin therefore sum up or partially account another contribution to the overall mineral for the current observed levels and continual

7 Philip and Mosha - Salt Lakes of the African Rift System …

regeneration/replenishment of the mineral An investigation of the stability of various reserves. This may explain why e.g. the soda soda ash minerals as a function of carbon ash mineral reserves such as Lake Magadi dioxide partial pressure ( P ) has been CO 2 may appear as defying depletion despite a undertaken, and this has revealed a variety lengthy (over 100-year) industrial of soda ash minerals as in Fig. 5 (Eugester exploitation history. 1970). Enumerated in the list for soda ash allied minerals typically encountered in Another modifier of the salt accumulation Lake Natron are: [NaCl], Nitratine mechanism and hydrochemical setting for 2+ [NaNO 3], [Na 3FSO 4], salt lakes is via early precipitation of Ca [KNO ], [Na CO .H O], and Mg 2+ carbonates and as well as 3 2 3 2 [Na 3H(CO 3)2.2H 2O], Pirsossonite fluoride to bedded sediments. This implies [Na Ca(CO ) .2H O] and Analcime alterations in terms of enrichment of bedded 2 3 2 2 [Na(Si 2Al)O 6.H 2O], for which examples of bottom sediments in terms of the less soluble the typifying identity and quantification, X- types, correspondingly depleted from the Ray Diffractommetry spectra, which aqueous electrolyte content above. featured and informed this work are shown in Fig. 6 (a) and (b). Natrocarbonatite type minerals: Stability and the governing temperature and pressure conditions

Figure 5 : The stability of various soda ash minerals as a function of carbon dioxide partial pressure ( P ). CO 2

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Tanz. J. Sci. 38(3), 2012

Figure 6 : X-Ray diffractograms of natural Tanzanian salt lake (L. Natron) soda ash evaporites yielding identity and quantification of the soda ash allied minerals. (a) A sample of soda evaporites sourced at Eng’onguremit – Gelai flats [36 M 0172227, UTM 9724083]. (b) Sample of embedded crystalline material below crystallizing brine sourced at Takano [36 M 0822186, UTM 9717446].

Lake volume shrinkage during dry months Seasonal and locational dependence of interprets into brine electrolyte electrolyte concentrations concentration increase. A representative example is Lake Natron, where in January

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2011, the authors observed an estimate of reverses in rainy seasons, leading to dilution. over 60% dry-up of the lake (Fig. 4b). In this As observed in Fig. 7, the highest brine season, the brine concentrations registered concentration during wet season was 314.5 Total Dissolved Solids (TDS) up to 24,900 ppm. ppm (Fig. 7). However, the situation

Figure 7. A map of part of the Lake Natron Basin showing sampling sites and respective brine concentrations (TDS in ppm). Wet season ( ) and dry season ( ).

Open lake brines register the maximum and/or inflow (streams, creeks, lagoons). electrolyte concentrations, while upstream Presence of aquatic life forms is an indicator sources (, streams, springs) show pointing to dilution influence for brines in progressive dilution in that order. Depth the locational vicinity. rarely, the constitution variance dependence is compass axis direction can prove a unimportant since these lakes have rather concentration gradient variables well, as nominal depths, often below the one-to-two testified by the Lake Natron case, where a metre depth mark. The salt concentration north- concentration trending is peaks maximizes and stabilizes in the ‘open occasioned by a major southward inflowing lake’ away from any diluting influence freshwater Ewasong’iro river whose lake

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diluting influence is maximum in the north, Quaternary systems replicating the brine but diminishes southward, with maximum ionic strength conditions and electrolyte brine concentrations attained towards the compositions in individual lakes were south in the Wosiwosi/Tokano salt flat studied at 30 °C, 40 °C, 50 °C and 70 °C so locations (Fig. 7). as to construct isotherms and derive phase diagrams using both the Teeple and Jänecké THE PHASE RULE TOOL IN SALT approaches for discerning the crystallization SEPARATION SCIENCE pathways starting with a replicated The phase rule serves the basics on which to constitutionally specified salt lake mother anchor the separation science for “useful” liquor (Sheshadri 1976). The Jänecké pure salts such as NaCl, Na 2CO 3, Na 2SO 4, version, (Fig. 8 (b)), lends itself to proven K2CO 3 and K 2SO 4 from the natural aqueous ease of interpretation in phase rule multi-electrolytes. Manifestation of nature’s separation science, and was used to design solubility equilirbia and the applicable successful crystallization paths revealing the principle(s), can, for example, include the following mother liquor-to-product schemes: “Bull’s eye pattern” which attends the (i) System NaCl + Na 2CO 3+ NaHCO 3 + drying-up progress for a salt lake. Here H2O yields trona, Na 2CO 3.nH 2O, crystallizations start with the least soluble on and halite. the periphery, systematically progressing (ii) System NaCl +Na 2CO 3+ Na 2SO 4+ H 2O inward under those governing principles yields burkeite, Na 2CO 3.nH 2O, ( 1938, Robertson 1929, Teeple 1929). sulphate and halite. (iii) System Na 2CO 3 + Na 2SO 4+ NaHCO 3+ Indigenous “pure salt” separation H2O yields burkeite, trona, nahcolite technologies have evolved around soda lake- and sodium sulphate. side populations, for example for the Katwe volcanic crater lakes of western The notation Na 2Cl 2 is a phase diagram (Arad and Morton 1969). The same is seen stoichiometry convenience (improvisation) in the L. Eyasi (Orr and Grantham 1931) and to cater for NaCl vis-à-vis Na 2CO 3 and Lake Kitangiri (Tulia Division 1999) cases Na 2SO 4. Based on our work, recovery in Tanzania where end-products of efficiency for a process design intended for exceptional purity were encountered. For the extraction of pure salts from a soda brine, chemical investigative work, it is needed to example , has demonstrated the carry out solubility equilibria studies in re- encouragingly excellent recovery profile constituted laboratory test multi-electrolyte (Table 4). Values (except for % recovery – brines to establish the crystallization last column) are in kilograms. pathways.

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(a) (b)

o Figure 8 : The quaternary system: NaCl + Na 2CO 3 + NaHCO 3 + H 2O at 50 C: (a) Teeple; (b) Jänecké version (Sheshadri 1976).

Table 4: Pure salt recovery profile for artificially re-constituted , Eyasi brine.

Salt Initial (mother liquor) Extracted Residue (bitterns) % Recovery NaCl 1362 1216 146 89.3

Na 2CO 3 188 136 52 72.4

Na 2SO 4 111 92 18 83.8

CONCLUSION from addressing quantity and quality, The promising mineral resource potential of hydrochemistry of natural hyper-saline the rift salt lakes in Tanzania has remained multi-electrolytes is scientifically rewarding, largely unexploited with no significant exciting and challenging, due to contribution into the national economy, fundamental departures from dilute aqueous which currently relies on importation for key systems, in terms of chemical processes and industrial salts, mainly carbonates, equilibria, that govern such systems. Critical , sulphates, chlorides and in such environments are the key alterations phosphates. These industrial salts are no in solubility, formation, sedimentation, ion- longer chemically manufactured, but solely solvent behaviour, toxicity of various forms, mined from salt lakes elsewhere globally. ecological mobilization and bioavailability Detailed scientific chemical knowledge of pathways for food webs in the ecosystem. these lake systems, beyond the scanty and Additionally, phase rule studies on outdated available in the literature, is a key separation of pure salts from lake brine interventional pre-requisite towards concentrates as demonstrated in this work, harnessing and prioritizing these resources. have a direct industrial value, and hitherto, Research targeting these knowledge gaps is only those indigenous extraction among the basics for this to happen. Apart technologies independently evolved by

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Tanz. J. Sci. 38(3), 2012

lakeside populations are in evidence. The Dissociation Constants of HF in salt minerals of these lakes, together with Concentrated Electrolyte Environments other resources of these rift systems, ought and Their Relationship to the to register their rightful and meaningful Thermodynamic Value. J. Chem. Soc. contribution to the national economy Pak. 18 : 96-100. through those strategies, apart from Mwakoba N, Mosha DMS and Schrøder K catalyzing quality academic research. 1992 A preliminary chemical survey of the salt deposits and evaporites of Lake REFERENCES Balangida, Hanang District, Tanzania. Arad A and Morton WH 1969 Mineral Tanz. J. Sci. 18 : 55-61. springs and saline lakes of the western Ngambeki WW 1996 A study of the rift valley, Uganda. Geochim. chemical constitution and hydrochemical Cosmochim. Acta. 33 1169-1176. equilibria in a concentrated salt lake: Bates RG 1948 Determination of the product Lake Eyasi . MSc Thesis, University of of the constants for the overlapping Dar es Salaam. dissociation of weak acids by Orr D and Grantham DR 1931 Some salt electromotive force methods. J. Amer. lakes of the northern rift valley zone. Chem. Soc. 70: 1579-1584. Geological survey of Tanganyika, short Eugester HP 1970 Chemistry and origin of paper No. 8 Government Printer, Dar es the brines of Lake Magadi, Kenya. Salaam. Mineral. Soc. Amer. Spec. Pap. 215-235. Qulwi QW 1995 A Study of the Gale WA 1938 Chemistry of the Trona Hydrochemistry of Brines and process from the stand point of the phase Associated Inflows of Lake Manyara . rule, J. Ind. Eng. Chem. 30 867-879. MSc Thesis, University of Dar es Guest NJ and Stevens JA 1951 Lake Natron, Salaam. its Springs, Rivers, Brines and Visible Robertson R 1929 The trona interprise. Plant Saline Reserves, Mineral. Res. Pam. of the American Potash and chemical Geol. Surv. Tanganyika . corporation at Searles Lake, J. Ind. Eng. Horne RA 1969 Marine Chemistry. The Chem. 21 520-548. Structure of Water and the Chemistry of Sheshadri K 1976 Phase Rule Chemistry of the Hydrosphere. Wiley-Interscience, Aqueous Salt Systems, CSMCRI New York. Bhavnagar, Gujarat, India. Kameka N 2006 The hydrochemistry of Teeple JE 1929 Industrial development of selected Tanzanian salt lakes and Searles lake brines. American chemical investigation of the potential for salt society monograph 49. Chemical Catalog separation in such systems . PhD Thesis, Co. New York. University of Dares Salaam. Tulia Division 1999 Lake Kitangiri Ward Mosha D, Qulwi Q and Mhinzi G 1996 Office, personal communication. Measurement of the Apparent

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