A giant dust devil greets us as we make our way to the northern cove of Lake Magadi. The surface on which it is swirling should be a greyish white — was actually a greyish white — until about 10 years ago, when it started acquiring a beige tint and then tanned. Now it is a mélange of brown hues, ranging from tan to chocolate.
The once cloudy rock of dense sodium carbonate brine, which precipitates to yield the mineral trona (sodium sesquicarbonate), the raw material for soda ash, is heavily contaminated with soil and debris.
Lake Magadi, which measures 164 square kilometres, is the largest source of natural soda ash in Africa.
However, at least 14 square kilometres of the mineable 52 square kilometres of the lake from which the mineral is mined are now unusable. That is about a quarter of the mineable area.
According to staff at TATA Chemicals, the firm authorised to extract minerals from the lake, this problem is caused by sediments carried into the lake by run-off believed to be from Suswa and Nairagie Enkare in Narok Country, about 100 kilometres away, which has for the last decade been interfering with the lake’s chemical processes to adulterate the crust of sodium carbonate brine as it forms.
On the patch where the effect is obvious, Mr George Otiende, a geologist at the firm, explains that the sediments have been infiltrating the trona regeneration process to form a contaminated version of the crystalised mineral from which soda ash is extracted.
TRONA RESOURCES
The mineral, which has been mined at Lake Magadi in the Kenyan Rift Valley for nearly 100 years, is the kind that regenerates after it has been mined.
The geography and geology of Lake Magadi are such that it is among the few places in the world where trona forms naturally.
Also referred to scientifically as sodium sesquicarbonate, it is deposited into the lake through lagoons and faults along the walls of the lake, which Otiende also explains acts as an evaporative pan.
The lake is recharged mainly by hot alkaline (40°C- 80°C) that is discharged along the lake’s marginal faults into lagoons bordering the lake.
Lying at the lowest point of the Rift Valley in a catchment area of faulted volcanic rocks, and with no permanent rivers entering the lake, only surface runoff, usually from the short and long rains experienced in this area, give rise to hot springs along the perimeter of the lake. It is these springs that feed the lagoons, which are perennial water bodies on the lake’s margins.
Trona is formed by the leeching of chemicals, including sodium carbonate or soda, washed down volcanic fissures on the valley’s walls made of igneous rocks that have undergone a long geological processes of weathering, break- down and erosion.
The chemicals released from these rocks are carried into the lake’s trough by the hot springs on the edges of the lake. When they come in contact with carbon dioxide, they precipitate as sodium carbonate brine.
With temperatures as high as 80°C and little surface run-off in this arid region, the lake acts as an evaporating pan, hence the solidification of the crystals into trona.
Mr Otiende explains that the trona deposits in Lake Magadi are constantly renewing themselves naturally. In some areas in the lake, the trona is up to 40m below the surface. Net annual accumulation of trona has been calculated to be 0.3cm to 0.4 cm, with variations between the wet and dry seasons.
After trona has been harvested, it takes 15 to 20 years for it to regenerate to maturity.
Mr Otiende notes that the vast amounts of silt had been gradually contaminating the brine during regeneration, affecting not just the quality, but also the rate at which it regenerates; the silt is said to be slowing down the crystallisation of the trona.
“Right now in areas where it has reformed with silt in it, it is no longer trona we can rely on for production,” he says.
The siltation has been gradual, occurring over the years, with the infiltration of the lake by run-off after a series of heavy downpours upstream. But the more recent escalation has been mostly as a result of flash floods in faraway Narok.
According to the geologist, the soils are deposited at the rate of 8,000 tonnes per hour during flash floods.
In April this year, a huge flood knocked down the wall of a dyke built on the northern creek to prevent the debris-laden floodwaters from entering the lake. It brought with it debris of cotton soil including shrubs, which have already started regrowing in the lake. The ingress remains agape, so should there be a downpour before the dyke is rebuilt, more floodwaters will find their way into the lake.
TATA,has been recording changes in the resource from which salt for human and industrial use is extracted. Insolubles in the soda ash have increased from an average 0.25 per cent in 2004 to 1.29 per cent in 2015.
QUALITY CONSCIOUS
The alkalinity level of the soda ash — the measure of quality for the mineral — has been declining steadily and now stands at 95 per cent, down from 97 per cent. Internationally, the ideal quality standard for soda ash is 99 per cent.
“When it has impurities, it affects the quality of the resultant glass products, making them susceptible to breakage, or making the glass hazy, and this has been a common complaint for the last two to three years,” explained TATA Chemicals’ mining production team leader, engineer Joshua Marabui.
Not only is the company incurring extra production costs as it attempts to clean the impurities, but it is also forced to charge a lower price for any product that doesn’t meet the expected standards.
As the Managing Director of TATA Chemicals, engineer Jack Muchira Mbui, explains, “Some of the stubborn impurities are insoluble so we can’t get them out, and that is where the major problem lies.”
We have to deduct a certain percentage on the value of our soda ash, depending on how low its total alkalinity has dropped from the ideal.
“This has led to the loss of millions of shillings through concessions on lower qualities of the mineral sold to our customers,” revealed the MD.
Yet, he points out, “Magadi operates in a very quality-conscious industry, as international manufacturers of glassware are very specific about the amount of impurities they can allow in their stocks as it affects the quality of glass they make.”
Mr Mbui says the situation creates an uncertain future for the nation’s prized soda ash mining industry as it faces competition from other natural producers like Botswana, China, Turkey and the United States, as well as producers of synthetic soda from China, India and Europe.
It is feared that the damage will not only affect the company, which is one of the few natural soda ash producers in the world, but also pose a threat to the entire lake’s ecological system, including flamingoes, which use it as a breeding ground.
The company has already been forced to compensate discontented customers, the MD said, leading to the loss of millions of shillings.
“The area that can be mined has shrunk significantly. We will have to cough up at least Sh200 million to shift each of the two dredge systems that we have on the side of the lake that is badly affected by the soils. There are trees growing there already.”
This menace, first noticed in 2005, is said to have been aggravated by several years of poor farming practices on the western side of Mt Suswa as well as the eastern side of the Mau ranges, which was previously covered by forest but later cleared for farming.
Area leaders, including Governor Dr David Nkedianye and Kajiado West Member of Parliament Moses ole Sakuda, attributed the problem to soil erosion as a result of deforestation and poor farming practices.
PLANTING TREES
“Over the years we have seen the havoc caused by the rains and together with TATA, we will mobilise residents to plant trees and have them educated on good farming practices,” Ole Sakuda said, adding that they had already established a tree nursery with 60,000 indigenous tree seedlings which they will plant in Suswa.
About 80 kilometres upstream, which is the lowest point of the Rift Valley at 600 metres above sea level, Tasilimo ole Punywa’s farm in Olesharo in Suswa has been divided into two.
It has a 50-metre wide and 30-metre deep gully running smack right in the middle.
It is through his farm that the flood waters flow on their way to the lake.
“To go to the other side of the shamba, I have to make a 20-kilometre journey.”
He blames the contractor who built the Mai Mahiu-Narok Road between 2005 and 2007 for the disaster he is witnessing on his land. TATA also partly blames the contractor. The miner started noticing changes on the northern side of the lake in 2005.
They both also agree that the diversion of water and construction of culverts directing water from Duka Moja and Suswa to the Maltauro Bridge is more than likely the genesis of their problems. It is these waters that have carved a direct channel to the lake.
Kajiado West MP Ole Sakuda says it is clear that an environmental impact assessment wasn’t done and points an accusing finger at the National Environmental Management Authority.
The MCA Suswa Ward in Narok East, Mr Kipas Lengues, who recently assessed the problem, says the gully resulting from the routing of water to this bridge stretches 80 kilometres into the lake, affecting more than 1,000 farmers on its path. Many farmers are said to have lost livestock in sections where the gullies have developed into ravines.
Mr Lengues says the problem is particularly bad when it rains heavily.
“When the rains come, they sweep carry with them all the top soil, which in this area is mostly volcanic, leaving devastation in their wake.
To make matters worse, the farmers are either not familiar with, or do not heed, good farming practices which include soil conservation, in slope cultivation. In this area, you will hardly see any run-off or soil erosion control mechanisms.
The staff at TATA are convinced that it is these poor farming practices and deforestation that are contributing to the scale of the problem they are faced with downstream and have promised to work together with the local governments to train farmers on improved crop management practices.
A few things make Lake Magadi one of a kind. It is one of few alkaline lakes, and is also one of the few used by flamingoes as a breeding ground.
The firm will distribute tree seedlings to farmers so that they can plant them in order to control soil erosion during rainy season. They are also building gabions to prevent the top soil from being washed into the lake.
TATA says it is considering creating check dams and desilting the existing dams upstream to stop further siltation, among other solutions.
The firm is also embarking on an environmental impact assessment as it considers changing the course of the seasonal River Kisamis upstream. If it is accepted, the river will be diverted to Oldorkoat Olonchakunai in Mosiro Ward to stop it from draining into the lake.
Soda ash is used mostly in glass making, but also in powderdetergents, medicine, as a food additive, in photography, in cleaning and boiler compounds and pH control of water.
At least 90 per cent of the soda ash from Magadi is exported, mainly to the Indian subcontinent, the Middle East and the rest of Africa.
Kenya is the third largest producer of the mineral in the world, and exports 90 per cent of the 320,000 tonnes it produces annually.
Trona is a compound that is processed into soda ash or bicarbonate of soda, as it is commonly known.
Lake Magadi is one on the few places in the world where trona forms naturally
Once mined, trona takes 15 to 20 years to regenerate to maturity
Kenya is the world’s third largest producer of trona.
No comments:
Post a Comment