Assessment of Distribution and Composition of Quarry Mine Dust: Case of Pomona Stone Quarries, Harare
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Abstract
The study aimed at assessing the distribution and composition of dust produced at Pomona Stone Quarry mine in Harare, Zimbabwe. The source contribution to ambient PM 2.5 and PM 10 dust levels were quantified and their spatial distribution from the quarry to the receptor (community). The study also analysed the pH of soils around the mine, SiO 2 and Al 2 O 3 levels in quarry dust. Data was collected through direct observations, personal communications, experiments, soil and dust sampling and analyses. Dust sampling was done in January, April and August, to assess the effect of meteorological conditions on dust concentrations in two phases. Phase 1 was conducted during plant shut down (baseline measurements) while phase 2 was carried out during full plant operations (normal operating conditions), to assess the effect of quarry operations on the surrounding areas. Within the quarry production processes, crushing stage was the most dust emitting stage. Phase 1 dust results showed that both respirable (PM 2.5 ) and inhalable (PM 10 ) dust at all stages were below the legal limit, thus below 35 mg/m 3 (respirable) and 180 mg/m 3 (inhalable). Highest dust levels (209.9 mg/m 3 inhalable and 69.01 mg/m 3 respirable) were recorded in August, followed by April (206.9 mg/m3 inhalable and 67.52 mg/m 3 respirable) then January (206.82 mg/m 3 inhalable and 65.27 mg/m 3 respirable). At all stages, highest dust concentrations for both parameters were recorded near the plant and decreased with increasing distance from the plant ( ranging from 209.9 mg/m 3 - 19.41 mg/m 3 inhalable and 69.01 mg/m 3 - 14.23 mg/m 3 respirable). This was attributed to the effect of particle size. August recorded the biggest area for both parameters falling within the non-permissible category, followed by April then January. The findings also revealed that the quarry dust contained higher levels of SiO 2 (0.752 mg/cm 3 ) which were 7 times higher than the recommended 0.1 mg/cm 3 (NSSA). Low Al 2 O 3 levels of 0.102 mg/cm 3 were recorded and this was considered as environmentally safe. Soils were slightly acidic-alkaline and the t-test results at 95% confidence interval showed no significant difference between the results from site A and B (p = 0.526). It was concluded that quarry dust from Pomona had no significant effects on soil pH but possible health impacts on the receiving community. The study recommended that dust suppression systems such as water sprays, vegetation, air nets and enclosed production process must be implemented to curb dust emissions.
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