Gamma Ray Spectrometric Analysis of Sedimental Deposits at the Shores of Lake Nakuru, Kenya

The main objective of this study was to assess human exposure to natural sources (U-238, Th-232 and K-40) of radiation on the shores of Lake Nakuru, Kenya. Gamma ray spectrometry of soil samples was done using NaI(Tl). The results obtained showed average activity concentrations of 36.9±9.1, 43.5±3.8 and 708±33.2 in Bqkg-1 for 238U, 232Th and 40K respectively. A total dose rate of 71.97 nGyh-1, annual effective dose rate (outdoor) of 0.088 mSv and average hazard index of 0.410 were obtained. The average dose rate for the northern sector was found to be 96.22±5.39 nGy/h while the southern sector has 26.69±0.69 nGy/h showing enhanced pollution at the northern sector. The findings from this study showed that radiation hazard from terrestrial naturally occurring radionuclides is low and human radiation exposure is within safe levels. Spatial difference in the activity concentration between the northern and southern sectors of Lake Nakuru was observed. There is need to closely monitor the northern sector and the rivers discharging water there in order to establish the source of the elevated activity. Keywords: Radionuclides, NaI(Tl) ?-ray Spectrometer, Activity concentration, Dose rate, Lake Nakur

Fluoride adsorption onto an acid treated lateritic mineral from Kenya: Equilibrium studies

Adsorption of fluoride (F) ions from water using acid treated lateritic mineral (LM-1) from Kenya was studied by batch experiments. The effect of acid-treatment of adsorbent and change in temperature, mass of LM-1, pH and selected competing ions was evaluated. The adsorption process was strongly influenced by temperature, pH and adsorbent dosage. The percentage F removal increased the presence of the nitrate and the chlorate ions but decreased the presence of sulphates, chloride and phosphate ions. Adsorption isotherms were classified according to Giles’ classification and the adsorption data validated using Langmuir and Freundlich isotherms. The data correlated to both the Langmuir and Freundlich isotherms although the data fit to the Freundlich model was somehow better. This showed that F adsorption onto LM-1 followed a mixed adsorption mechanism in which physisorption reactions involving intra-particle diffusion of F into mesoporous sites in LM-1 became increasingly important at higher concentrations and temperatures whereas ion-exchange mechanism involving surface OH- appear to dominate at low surface coverage in more alkaline conditions. With maximum adsorption capacity of 10.5 mg/g, LM-1 could be used to remove F water.Key words: Equilibrium analysis, fluoride adsorption, Langmuir and Freundlich isotherms, Lateritic mineral adsorbent, low-cost adsorbents

Results of injection and tracer tests in Olkaria East Geothermal Field

This paper presents results of a six month Injection and Tracer test done in Olkaria East Geothermal Field The Injection tests show that commencement of injection prior to onset of large drawdown in the reservoir leads to greater sustenance of well production and can reduce well cycling which is a common feature of wells in Olkaria East Field. For cases where injection is started after some drawdown has occurred in the reservoir, injection while leading to improvement of well output can also lead to increase in well cycling which is a non desirable side effect. Tracer tests reveal slow rate of fluid migration (< 5 m/hr). However estimates of the cumulative tracer returns over the period of injection is at least 31% which is large and reveals the danger of late time thermal drawdown and possible loss of production. It is shown in the discussion that the two sets of results are consistent with a reservoir where high permeability occurs along contact surfaces which act as horizontal "fractures" while the formations between the "fractures" have low permeability. This type of fracture system will lead to channeled flow of injected fluid and therefore greater thermal depletion along the fractures while formations further from the fracture would still be at higher temperature. In an attempt to try and achieve a more uniform thermal depletion in the reservoir, it is proposed that continuous injection be done for short periods (~2 years) and this be followed by recovery periods of the nearly the same length of time before resumption of injection again