176 • Marine Minerals: Exploring Our New Ocean Frontier 



Figure 5-7.— Bucket Wheel Suction Dredge 



Hoist 



Discharge line 



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=m 



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Power 



-Spud 



Dredge 

 pump 



Bucket 

 wheel 



Suction ^ 

 line 



Bucket wheel dredges have been used primarily in calm inland waters. Equipped with motion compensation devices, these 

 dredges may have some potential for mining offshore placer deposits. 



SOURCE; Dredge Technology Corp. 



Bucket Wheel Suction Dredges 



The bucket wheel dredge (figure 5-7) is a vari- 

 2int of a cutter head dredge, differing mainly in that 

 the cutter is replaced by a rotating wheel equipped 

 with buckets that cut into the dredging face in a 

 manner similar to a bucket ladder dredge. The 

 buckets are bottomless and discharge directly into 

 the suction line. 



Bucket wheel mining dredges are a relatively new 

 development and have been used primarily in calm 

 inland waters. Some applications include tin min- 

 ing in Brazil, sand and gravel mining in the United 

 States, and heavy mineral mining in South Africa. 

 The bucket wheel dredge has not been used in the 

 EEZ, but it may have potential for mining offshore 

 heavy minerals in specific applications. Motion 

 compensation, offshore hull design, and mobility 

 would need to be considered. These dredges are 

 less effective when cutting clay-rich materials, which 

 may clog the buckets, and when dredging boulders, 

 which could block the opening into the suction lines. 

 However, bucket wheel dredges are more suitable 



than cutter head suction dredges for mining heavy 

 minerals, since the bucket wheel avoids the prob- 

 lem of loss of heavy minerals on the bottom. 



Air Lift Suction Dredges 



In airlift suction dredging, air under pressure is 

 injected in the suction line of the dredge, substi- 

 tuting for the mechanical action of a dredge pump 

 (figure 5-8) and creating suction at the intake which 

 allows the upward transport of solids. Airlifts have 

 been used for many years in salvage operations and, 

 during the past 25 years, for mining diamond-bear- 

 ing gravels off the southwestern coast of Africa. 



The technology of airlift dredges has not reached 

 the level of development and widespread use of the 

 other forms of suction dredging, but the configu- 

 rations are similar. Much research has been done 

 on the physics of the flow of water, air, and solids 

 mixtures in airlift suction dredging, because this 

 method has been considered one of the most prom- 

 ising for.dredging phosphorite or manganese nod- 

 ules from great ocean depths. In general, applica- 



